Liqiuid sitting in reciever

[bernard]

Hi


I have a recently installed scroll pack and condenser on the roof of a supermarket.

The reciever is full but when I look in the sight glass I see the liquid in the bottom of the 1 3/8 liquid line trickling past.The drier is good,Head pressure 13 bar suction 2.7 bar.If I increase the head pressure the sight glass clears for a minute then returns to a trickle.Is this just lack of demand on pack or ????.



Regards Bernard

[Peter_1]

No, only a lack of subcooled liquid, that's all.
When it passes through the sight glass, due to the velocity of the liquid, you have a small pressure reduction which forms flash gas.
Be carefull if the reciever is full while running: you propably won't have enough storage capacity in the reciever when all the units will shut down.

[Peter_1]

Bernard, what's +/- the capacity of the system?
Just to recalculate once the size.

I think I gave you wrong information: i thought that you meant with trickle that you were seeing bubbles in the liquid and that they disappeared temporarily when increasing pressure.

But if I re-read your first message now, you only see a bottom of liquid passing through the sight-glass.

Mostly you see this with an oversized condenser, low outside temperature and a rather big demand for cooling.
I always explains this to my son as there is much more refrigerant pumped by the compressors from the evaporators then there's feed toward the evaporators.
The driving force to the coolers is not big enough.

So you need to increase pressure and/or increase subcooling.

But you only can gave partial gaseous refrigerant in your 100% departing liquid if the liquid is just at the edge of being not subcooled (just at the saturation line) and there's a very slight pressure increase (or temperature increase which isn't the case here) .

But, at low ambient as you have now, or/and during low load conditions, refrigerant velocity is low because enthalpy is increased, so pressure decrease will also be low during cold ambient.

Something must be wrong with my thinking.

My son just told me a similar phenomena: when load is low during cold and very cold ambient, you see liquid flowing through a vertical mounted sight glass and many times, you see that it fills just halfway.
Why just there and why +/- halfway the sightglass?
Why not lower or higher somewhere in the liquid line.

But it intrigues me also that I haven't THE answer for your question. So I will follow this post very close.

[bernard]

Yes Peter I have suspected the condenser is oversized,I will find out the capacity of the equipment,I have no experience with sizing.

I took the head pressure up to 15 bar,but this did not clear it so its back at 13 bar,I can forsee problems over the winter with this site unless I can cure it.


Regards Bernard

[chemi-cool]

I'd go with Peter way of thinking,

sound as the components are not all in the right size,

do you have any way to check it out?

Chemi

[bernard]

Hi Chemi

I will take all the plate details of the eqipment and post them here.

Regards Bernard

[monkey spanners]

Has the sight glass ever been full? If not is it possible that the reciever is piped up with the inlet as the outlet and hence no dip tube?
How much refrigerant is charged into it compared to the design charge?
Maybe what my old boss used to call overcondensing, too low a liquid line pressure/temperature, or am i showing my ignorance again

Cheers Jon

ps my old boss also used to say i belonged up a tree on the newbury bypass

[Mark]

Is the reciever sized so system charge can be pumped down?.

[US Iceman]

Bernard,

If I might ask... How do you know the reciever is full?

[Mark]

Bit of a grey area,sometimes reciever data plates can be a misleading way of determining total charge.

[NoNickName]

No, the charge here is done depending on subcooling. Same size of unit can have a difference of +/-10% depending on manufacturing tolerances.
I ripped the balance off the testing department. They have to look at manometers and thermometers, not at Kgs.

[Mark]

This thread opens another question.

Determining an existing Pack install refrigerant charge.

Without reclaiming and weighing

[Andy]

Hi Bernard

I have seen this too It happens during low load situation. In theroy it should happen when you have a cold receiver, where the charge wants to stay in the coldest spot. But I have seen in on housed acoustic packs with the receiver mounted on the pack.
From what I understand it's a good example of lanier (non turbulent) flow. This is due to the velocity of the refrigerant in the piping (the pipe is much too large for the duty at that point).

Hope this helps

Kind Regards Andy

[NoNickName]

This thread opens another question.

Determining an existing Pack install refrigerant charge.

Without reclaiming and weighing

One simply can not

[bernard]

Hi All


Sorry for the delay on my response as I,m on call at moment,I must also point out that there is no problem with case temps.

To answer a few question before I go out again The reciever has two bullseyes lower and upper part of recievers to indicate level.

Reciever is piped correctly as I also suspected this.

Hi Andy this lanier flow you mention,could this happen if the defrost schedule was incorretly spaced so at certain times of the day demand was low.

I was on site at 4am on another job and noticed the sight glass was full,I have the makes and models of all equipment Is it worth posting or not.


Regards Bernard

[US Iceman]

HI Bernard,

Thanks for the feedback. Since the receiver has bulls-eyes and they indicate the receiver is full (as best as you can see), this would indicate the system has been pumped down, or at least partially.

This in itself brings up an issue as to whether the receiver has sufficient volume to accomodate a full pump down and still have at least 20% volume available as a gas space in the receiver.

On the other hand, if the receiver is showing full (at least to the top bulls-eye) the small trickle of liquid flowing through the main liquid line site glass would indicate a very small demand in relation to the maximum flow capacity of the pipe.

This would produce a condition known as laminar flow, and as Andy mentioned this type of flow is non-turbulent. In laminar flow the liquid (in this example) is essentially moving very slowly, so I would expect some areas of the pipe to not fill completely.

The low load condition which could cause this can be attributed to low demand (very little capacity required).

This could be from either the case temperatures being satisfied with only a very small load being present, or a majority of the cases being in defrost simultaneously.

As you said, the case temperatures are OK which leads me to believe the condition you are seeing is due to low load (or defrosts occuring together) at that precise time.

If the receiver is full and the system must operate during cold weather, what type of discharge pressure control does the system have?

The reason I ask is... If the condenser has controls to flood the condenser for cold weather operation, will the receiver or refrigerant charge be large enough?

[bernard]

Hi Thanks for your last post

Head pressure is controlled with a Danfoss EKC 531B Capacity Controller via pressure tranducers.


Regards Bernard

[markh]

im new to this posting lark, but being a commissioning engineer i would look at a couple of things and take these points into consideration.
firstly, if the plant is 1 or 2 floors above the cases/coldrooms you may have a suction pressure drop ,if so drop the target suction pressure down,increasing duty on the pack.Secondly ,check the stage delays on the pack.
Also, check the transducers are callibrated correctly as i have had a lot of them 1/2 to 1 bar out.

[markh]

sorry feel like a complete donut as i didnt see the second page! defrost settings are critical but i will say that certain supermarkets will demand the site defrosts in islands so there aint a lot you can do if its one of them!

[Peter_1]

This would produce a condition known as laminar flow, and as Andy mentioned this type of flow is non-turbulent. In laminar flow the liquid (in this example) is essentially moving very slowly, so I would expect some areas of the pipe to not fill completely.

If 100% pure liquid is departing from the vessel, why you see then 2 inches further in the liquid line at a sudden gasseous refrigerant?

I understand we can have a laminar flow but how is this 2-state refrigerant then formed?

I said previously, this is something I saw so many times and I never had THE answer for it.
As soon as you block the condensor with a paper, it disappears and sometimes, it comes back even with the paper in place in front of the condensor.

[US Iceman]

Hi Peter,

I understand we can have a laminar flow but how is this 2-state refrigerant then formed?

My thought was the pipe is not flowing full, so the clear area of the site glass was simply a lack of liquid refrigerant flowing. In other words, there is not enough refrigerant flowing to fill the pipe.

I have seen this exact thing before many times also and it always seemed to coincide with low load operation, or other conditions which simulated low load conditions.

Placing a piece of paper over the condenser would increase the discharge pressure, so the pressure differential across the TXV would increase. The valve temporarily gains capacity so more refrigerant would flow, thus maybe filling the pipe more.

I seem to remember this is also seen with air-cooled condensers in the winter time if no head pressure controls are used.

With very low head pressure there is not a sufficient pressure differential to get the TXV to open enough. Even with the compressor running I believe the same low site glass flow was seen then.

That's my best guess right now.

[bernard]

Hi

So in low load conditions does this mean that the cases in demand are not being supplied with a full bore of liquid.

Regards Bernard

[DANIEL ARYEE]

Hi


I have a recently installed scroll pack and condenser on the roof of a supermarket.

The reciever is full but when I look in the sight glass I see the liquid in the bottom of the 1 3/8 liquid line trickling past.The drier is good,Head pressure 13 bar suction 2.7 bar.If I increase the head pressure the sight glass clears for a minute then returns to a trickle.Is this just lack of demand on pack or ????.



Regards Bernard

HI MY NAME IS DANNY. I WILL LIKE TO KNOW THE KIND OF REFRIGERANT YOU HAVE IN THE SYSTEM. I MAY BE ABLE TO HELP.

[bernard]

Hello Danny

Its refrigerant 404a

Regards Bernard

[US Iceman]

So in low load conditions does this mean that the cases in demand are not being supplied with a full bore of liquid.

Hi Bernard,

If I can turn this around some, I think the site glass appears to have this condition when the demand is low. If the demand is lower then you would have less refrigerant flow through the liquid line (which is now much larger than it needs to be for the reduced demand).

If the refrigerant mass flow is reduced, then the volume flow would also be reduced, hence the lower level in the site glass.

There may be sufficient refrigerant to feed the lower demand requirements (fewer cases/coils in operation).

I've also seen this on some systems where the discharge pressure is too low to feed liquid to the TXV's. There may be enough load to keep the compressor running on the LP switch. However, the discharge pressure could be just low enough to only allow a minor flow of refrigerant. This would eventually show up as a loss of temperature control for the space.

If the TXV's are only partially open due to low differential pressure they will not be feeding a lot of liquid. In this case, the liquid would back up into the receiver as if the system were pumped down.

These are the only times I have seen this type of incident occur.

What I don't know is the operating conditions of the system when you noticed this. If the day was much cooler, the discharge pressure control setpoint may have been too low. In effect, this could starve the coils due to the lower differential pressure available to obtain valve capacity.

If the system has multiple evaporators, were a majority of the coils off on temperature? This could then say the demand was lower with smaller or less coils in operation.

Does that make sense?

[bernard]

Yes the was ambient was lower than normal due to high winds.How high do you think I can take the discharge set-point as 14 bar is higher than any other packs I have.

I was chatting to the in store tech who does the case cleans he said all the coils he washes are only iced up in the pack 2 or three passes.I,ve had that problem before and increasing the head pressure cures it.

I,ve been told in the past I look to deep into things,But the way I see it is a problem will find you sooner than later so its best to find it before it finds you.At the moment its a case he who shouts loudess gets served first.

I was there yesterday the reciever float was at the top of the upper buulseye,the sight glass was full/large bubble.I think I will recover some refrigerant,the recievers hold 115 litrs.

There an on-going problem with the monitoring system so accsess to to graph for evap and suction temps is out.

Thanks Bernard

[US Iceman]

I was chatting to the in store tech who does the case cleans he said all the coils he washes are only iced up in the pack 2 or three passes.I,ve had that problem before and increasing the head pressure cures it.

What changes when the head pressure is increased? Obviously, the pressure increases so I suppose this affects something. It could be the higher pressure differential for the TXV.

It's been almost 20 years since I have done any real service work so I'm sort of rusty. But I seem to think a TXV with continued low head pressure will cause an inordinate amount of frost to form on the first few coil passes. With low head pressure the valve will not open enough, so the little bit of refrigerant that flows through the valve is all evaporated on these first few passes. Hence the heavier frost patterns. Once all of the liquid is evaporated you only have gas which just superheats.

I'm not familiar with controller you said was installed. Is it just a fan cycling switch of sorts?

The other thing could be the TXV's. I really like the balanced port valves as they react very good to low head pressure operation if they are selected correctly.

Are the valves that are installed balanced port valves? If they are not, and you only have fan cycling control for head pressure this could be part of the problem.

I think this is a good discussion and would like to see some input from others about their experiences with this.

But the way I see it is a problem will find you sooner than later so its best to find it before it finds you.

I call that pro-active. Or another way to phrase it is... do something before it bites you.

[Peter_1]

What changes when the head pressure is increased? Obviously, the pressure increases so I suppose this affects something. It could be the higher pressure differential for the TX.

What also changes is the following (I think): the receiver is full of liquid and also the steel of the receiver has the same temperature. So we're in a saturated state and there's not so much movement in the liquid and there are also no big changes in load.

If we at a sudden increase pressure by stopping fans, restricting the air flow over the condenser, then we're going temporarily straight up in the log/P diagram, so making mechanical a bigger subcooling.

This increased subcooling will remain the same and slowly reduce till all the now warmer entering liquid in the receiver has mixed with the remaining colder liquid and the steel of the receiver has risen to this new 'mix-temperature' at a higher equilibrium temperature.

So the gaseous phase disappears due to a sudden increase in subcooling. (it's in fact not a real subcooling, USIceman mentioned some weeks ago a special term for this phenomena)

[US Iceman]

This increased subcooling will stay and slowly reduce till all the warmer entering liquid in the receiver has mixed with the remaining colder liquid and the steel of the receiver has risen to this new 'mix-temperature' at a higher equilibrium temperature.

WOW! Thats really a very good translation from Dutch to English Peter. I'm envious of you.

I read the discussion you and Dan had on the SI vs IP units for the posted threads and keep forgetting that you have to translate twice for some of us (SI vs. IP & English to Dutch).

You do such a good job on the language translation it is hard to remember (at least for me) that you have two steps.

[Dan]

My son just told me a similar phenomena: when load is low during cold and very cold ambient, you see liquid flowing through a vertical mounted sight glass and many times, you see that it fills just halfway.
Why just there and why +/- halfway the sightglass?
Why not lower or higher somewhere in the liquid line.

I have seen precisely what your son describes many times on Hussmann Superplus racks. I have also seen what was origianlly described in horizontal sightglasses... we call it a "lazy sightglass."

To be honest, the 1/2 full sightglass in the vertical line still mystifies me. How does the liquid ever get above the sightglass I ask myself.

But besides the mysterious aspects, we are seeing a saturated liquid. A bubbling sightglass is a high velocity saturated liquid and a "rivering" or "lazy" sightglass is a low velocity saturated liquid.

I wish it were the only mystery confronting me in this wonderful trade.

[Dan]

So the gaseous phase disappears due to a sudden increase in subcooling. (it's in fact not a real subcooling, USIceman mentioned some weeks ago a special term for this phenomena)

By all definitions of subcooling it is real. I think Iceman used the word "unfavorable" versus "favorable". When we speak of physical properties such qualifiers are unnecessary and confusing. Increasing pressure on a liquid without any other changes, causes the liquid to be subcooled. Period.

[US Iceman]

To be honest I don't remember what I called it. Too many things to store on the hardrive in my head (at least that is how I prefer to see it ).

Subcooling is normally easy as most people think of it in terms of the liquid being cooled at a constant pressure. Since the temperature does change in this instance the term subcooling is easily understood.
(temperature dependent)

On the other hand, if the liquid pressure is increased and the temperature does not change the liquid is still subcooled. (pressure dependent)

This is the type of subcooling (pressure dependent) that sometimes confuses people since the term subcooling is usually related to a temperature change. I think is what Peter is describing as "not real subcooling" from one of my earlier posts. It is indeed subcooling, NOT just the type of subcooling people usually think of first.

This can be as confusing as superheat (sometimes it can be considered useful, other times it can be considered non-useful). It depends on how the superheat affects the Net Refrigeration Effect per pound (or kg) and the specific volume of the refrigerant for the compressor performance.

In the example of superheat these qualifiers are indeed the correct ones to use. In attempting to describe the different types of subcooling I may have created some mis-leading terminology.

I believe if we think of subcooling in terms of temperature or pressure dependent it may be more clearly understood.

[Dan]

Ah... that's what you called it. Not Favorable/non-favorable, but Useful and non-useful. Pressure dependent or temperature dependent are good qualifiers as well.

But let the definition stand by itself:

Superheat is the difference between the temperature of a gas above the boiling temperature of that gas at a common pressure.

Subcooling is the difference between the temperature of a liquid below the condensation temperature of that liquid at a common pressure.

Qualifiers are fine as long as they add context to a term. But the definitions of subcooling and superheat must stand alone. Each represents a relationship of temperature and pressure to a fluid. And there are some confusing and misleading definitions abounding. For example, in Websters:

"Superheat: To heat a liquid above its boiling point without converting it into vapor." The truth is that such a liquid is subcooled. That is, of course until you take the cap off the radiator.

Whether a superheat or subcooled status is useful or not, or detrimental or beneficial, is purely a contextual qualification. Gravity is bad when I am dropping from an airplane without a parachute, but good when it draws me back to earth when I jump. But as a force it does not require qualification.

Superheat and subcooling are simply relative states that have no implications toward good or bad, enthalpy, or net refrigerating effect.

3 degrees superheat is wonderful at the outlet of an evaporator, but frightening at the inlet of a compressor.

30 degrees subcooling sounds like a good thing, but it would be better to reduce it to a minimum by lowering the pressure on the liquid.

It's the old tech writer in me that causes me to be such a pain in the ass. I only argue such fine points with those whom I have the highest regard.

[US Iceman]

Hi Dan,

I certainly don't find any fault with your basic definitions of subcooling or superheat. Those are what we have used for a long time and were probably taught in our formative years.

The definition from Websters is totally misleading.

The main issue I think is how to describe the different methods of obtaining subcooling. Peter has said this before, but I will repeat again.

On a P/H chart when the state point is in the liquid region an increase in pressure will create subcooling. That is absolutely true and based on good theory.

The problem lies in the fact that the actual liquid temperature has not changed, which is what the definition of subcooling presents, i.e., a temperature change.

We have in fact created a riddle which can be misunderstood.

I believe the problem arises when we forget to use the term "saturated" when dealing with pressures and temperatures. In effect, what we call temperature is not entirely correct. As with most things we work with there are two of everything.

Temperature is another variant of where qualifiers should be used, so I'll add to the already stirred pot.

Actual temperature or saturation temperature.

The actual temperature of course describes the exact temperature that can be measured with a thermometer.

Saturation temperature on the other hand can be found by the use of a P/T chart or P/H diagram. It however can also be found when the liquid/vapor co-exist in equilibrium. At this point, the saturation temperature becomes the actual temperature.

My basis of thought on all of was developed during my days doing service and later reinforced when performing system designs.

At any point in a refrigeration system we have pressures and temperatures co-existing. Always.

In finding problems we need to understand how these interact and their relative effect and impact on component performance (TXV's, compressors, condensers, piping, etc.).

Most people who have not worked on screw compressors have never heard the term discharge superheat. Most however, know what evaporator superheat is.

"Discharge" and "evaporator" are qualifiers for where the superheat is being determined.

"Useful" superheat occurs in the evaporator as it contributes to the Net Refrigeration Effect.

"Non-useful" superheat is just that. It is just adding heat to the vapor which provides no benefit to the system performance. In fact, this "type" of superheat lowers the performance of the compressor by increasing the specific volume of the vapor, which in turn reduces the mass flow circulated.

So... What I think this can be summarised as... we need to be careful when describing this pressure/ temperature relationship of the refrigerants.

The qualifiers we use to describe the various state points in a refrigeration system are useful in describing the actual operation.

They also help to find the problems after the system is installed, or help to prevent the problems from being created during the initial system design.

It's the old tech writer in me that causes me to be such a pain in the ass.

It's the old service man in me that makes me like this!

[Dan]

So... What I think this can be summarised as... we need to be careful when describing this pressure/ temperature relationship of the refrigerants.

Yes, Mr. old service man.

We should simply use pressure temperature relationships.

And we should record where we took each measurements.

And we should pretty much let these measurements stand proudly for analyisis alone. Neither useful, profitable, good, bad, indifferent, etc.

Proud and solid measurements whose stripes are in pressure and temperature relationships... hopefully in the proper units of measurements to be understood by the technicians on call.

I have not weighed my position lightly. Subcooling and superheat must stand alone as pressure-temperature relationships. We can add the qualifiers only after purity of measurement. There is no such thing as false subcooling because non-condesnibles might exist... there is no such thing as reverse superheat when the pressure is measured in the wrong place.

There is no "useful" subcooling, or other adjectives to be applied to superheat.

Subcooling and Superheat measurements must be without adjectives, opinions, or desires.

They can only come after seeing an accurate pressure-temperature relationship with a known fluid.

This has to be the firm ground we stand upon when discussing refrigeration.

[US Iceman]

Hi Dan,

I just saw your reply. I have not been ignoring you.

It is not my desire to beat a dead horse, but I'll wrap up my comments with the following statements.

Some of the measurements and methods of explanations I have used in this discussion are my attempt to show some of the strange findings that can be discovered during service or design processes.

All of these are founded on the refrigerant properties and/or the way the refrigerant interacts with the system in operation (or by design or installation).

Any adjectives used are solely meant as a poor attempt (on my part) to describe some of these unusual behaviours and the strange ways they might affect the system operation.

In closing up with this I'll add some final thoughts... Most of the stuff we have been taught is correct, but I will go and remain on record by saying, there are some strange things that can happen in a refrigeration system that can be difficult to explain without reverting to various means.

All in all, this has been a very good discussion.

[Dan]

All in all, this has been a very good discussion.

I agree. And please do not think that I do not respect your concern for "non-useful" subcooling or "none-useful" superheat. Once we stand on the firm rock of accurate measurements, your qualifications are essential in further analysis and discussion.

And yes, there are strange things that can happen in a refrigeration system that can be difficult to explain without reverting to various means. My example of non-condensibles causing subcooling is a wonderful instance of a phenomenom that I have difficulty explaining even to myself, let alone to others.

[US Iceman]

Once we stand on the firm rock of accurate measurements...

This is absolutely essential, otherwise it's just and argument for the sake of arguing when trying to discuss this stuff.

Some of this is very close to the following...

Is a peanut a vegetable or a nut to a squirrel? The squirrel might say, who cares?

[Dan]

Is a peanut a vegetable or a nut to a squirrel? The squirrel might say, who cares?

Precisely. Because we call it a nut and use it as a nut in our mixed nut cans, no wonder squirrels really prefer grade A corn.

[Dan]

I promise. I am stopping now. This was a fun discussion though!

[taz24]

And yes, there are strange things that can happen in a refrigeration system that can be difficult to explain without reverting to various means. My example of non-condensibles causing subcooling is a wonderful instance of a phenomenom that I have difficulty explaining even to myself, let alone to others. [/quote]


I'll give you strange things that happen in a fridge system.
Liquid in a receiver is subcooled. The vapour therefore cannot exist above it - but it does.
Liquid in a eceiver is subcooled and yet it is in contact with vapour

Cheers taz

[Peter_1]

Liquid in a receiver is subcooled. The vapour therefore cannot exist above it - but it does.
Liquid in a eceiver is subcooled and yet it is in contact with vapour

??Liquid in a receiver is mostly in a saturated condition, reason why gas and liquid can be seen together in a receiver. This seems very logic for me.
In the log/P diagram, gas and vapour can be found together at same temperature and same pressure, so...???

[Andy P]

We should simply use pressure temperature relationships.

And we should record where we took each measurements.

This thread is in danger of becoming a loop - Dan made the point very well a few posts ago that the readings you take can be at best meaningless and at worst misleading if you don't know where they came from. Don't forget that some changes in refrigeration systems happen pretty much instantly - eg pressure increases - whereas others are time dependent - eg heat transfer through liquid.

You might have the appearance of subcooled liquid in a receiver along with gas if either
a) the liquid at the surface is at the saturation temperature but the lower level liquid is colder and the temperature has not had time to equalise, or
b) if there is air in the system - hence the talk in earlier posts about non-condensibles and "apparent" subcooling

I was told years ago that the most useful bit of kit for a service tech would be a pair of the X-ray specs you used to see advertised in Marvel Comics (did anyone ever buy a pair???) In the absence of these you need to make do with a combination of a vivid imagination and Sherlock Holmes' famous saying "Eliminate the impossible, and whatever remains, however improbable, is the truth." Don't be fooled into failing to differentiate between the truly impossible and the norm in refrigeration - good old fashioned "misleading".

A bucket of ammonia is a good example: if you take a standard metal bucket half full of liquid ammonia and sit it in the open air the liquid will not boil off rapidly, but will sit quietly in the bucket looking like water. Why? If you measure the temperature of the liquid in the bucket it will be about -50 oC (-58 oF). Why? Ammonia is supposed to boil at -33 oC at atmospheric pressure....

cheers
Andy P

[taz24]

??Liquid in a receiver is mostly in a saturated condition, reason why gas and liquid can be seen together in a receiver. This seems very logic for me.
In the log/P diagram, gas and vapour can be found together at same temperature and same pressure, so...???

Yes same pressure and temp = saturated state.
But liquid in the receiver is subcooled. Liquid at a lower temp than the condensing temp is subcooled.
Liquid coming out of the condenser is subcooled, liquid in the liquid line is subcooled so liquid in the receiver is subcooled.

Cheers taz.

[US Iceman]

Here is a nice pearl of wisdom to remember when working on refrigeration systems. It ties in nicely with the comments of Andy P. Text courtesy of Wikipedia...

Occam's razor (also spelled Ockham's razor) is a principle attributed to the 14th-century English logician and Franciscan friar William of Ockham (Guilhelmi Ockam and Guillermi de Ockam in Latin [1]). Originally a tenet of the reductionist philosophy of nominalism, it is more often taken today as a heuristic maxim that advises economy, parsimony, or simplicity in scientific theories.
Occam's razor states that the explanation of any phenomenon should make as few assumptions as possible, eliminating, or "shaving off," those that make no difference in the observable predictions of the explanatory hypothesis or theory. In short, when given two equally valid explanations for a phenomenon, one should embrace the less complicated formulation. The principle is often expressed in Latin as the lex parsimoniae (law of succinctness):

entia non sunt multiplicanda praeter necessitatem,

which translates to:

entities should not be multiplied beyond necessity.

(That is, the fewer assumptions an explanation of a phenomenon depends on, the better it is.)
Furthermore, when multiple competing theories have equal predictive powers, the principle recommends selecting those that introduce the fewest assumptions and postulate the fewest hypothetical entities. It is in this sense that Occam's razor is usually understood.

I was told years ago that the most useful bit of kit for a service tech would be a pair of the X-ray specs you used to see advertised in Marvel Comics (did anyone ever buy a pair???)

I never bought a pair, but still remember seeing the advertisement.

Another good visualization technique is to imagine one molecule of refrigerant flowing through the system and the changes in pressure and temperature that can occur.

[winfred.dela]

. . .
Another good visualization technique is to imagine one molecule of refrigerant flowing through the system and the changes in pressure and temperature that can occur.

Thanks US Iceman,
It's nice piece of advise to simplify and understand it easily.

Been following this thread and it is becoming kind of like the thread Liquid Receiver:

http://www.refrigeration-engineer.co...iquid+receiver

[US Iceman]

Yes, it seems like we have been having guite the go on the receiver subject lately. It's amazing how much fun you can have on such a simple vessel.

[taz24]

Iv'e seen a 7kg dumpy used as an extra receiver once. It was working well, the two valve on top one for liquid in and the one with the dip tube for liquid out.

Cheers taz.

[US Iceman]

Iv'e seen a 7kg dumpy used as an extra receiver once. It was working well, the two valve on top one for liquid in and the one with the dip tube for liquid out.

Now don't take this the wrong way, but I would be a much happier camper if this sort of practice was not advertised or posted.

Before you know it, someone else will start to do this since they saw it posted on the RE site and the next thing you know... more people are doing it.

It's hard enough to get people to do it right without giving them information on how to do it improperly.

[taz24]

It's hard enough to get people to do it right without giving them information on how to do it improperly.[/quote]

Ok point taken

I will pay at little more attention to what I post.

Cheers taz.