A fellow engineer insist on fitting a crankcase pressure regulator to every system we install.
I beg to ask, Is it always necessary??
What conditions are necessary to warrant the provision of one
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A fellow engineer insist on fitting a crankcase pressure regulator to every system we install.
I beg to ask, Is it always necessary??
What conditions are necessary to warrant the provision of one
I only use it with hot gas defrost to protect the compressor from flood back.
I don't see any reason to use in every system.
Chemi:)
Thasnks Chemi.............
Youve answered my question..........
Now I know.........
That it is Not a necessity............
I have hardly ever used hot gas defrost
:)
Hi Aiyub,
The only time I have ever used a crankcase pressure regulating valve is for applications where the the system has a potential for high suction pressure starting.
If the suction pressure is operating within a reasonable range you should not need one of these.
I agree with Chemi on the hot gas defrost requirement too.
What sort of equipment is he fitting it to or should I say what is the equipment used for ??
Maybe he has stock in the company:D
:cool: Use them on freezer c/rooms, thats a while ago with R502, well cases etc used to use them alot on long pipe runs ie: super market jobs with condensing units.
I've recently been looking at a Freezer Room which refuses to pull down to -20 degrees C. It's an old Dorin belt drive unit charged with R408a ( I guess it was originally R502)
Somebody has fitted a Danfoss Crankcase regulator valve(CCPRV) in the Suction line.I think it's big enough not to affect the performance too much but when I look at the suction pressure even after 1 hour running time after a defrost there's still a slight pressure drop across the valve.
My question is : Would it be better to remove the CCPRV and fit a liquid line solenoid valve and reconfigure the system to pump down at each defrost. Defrost termniation on evaporator pressure has been removed...The original Paragon control ( with pressure override) has been disconnected from evap. pressure override for defrost termination. I'm trying to get my customer to agree to letting me fit an Electronic controller to the system.I.E. with defrost ( coil ) temp. termination and fan delay time after defrosts ( he's a bit on the mean side! He has 20 thousand dollars worth of stock in his freezer and complains every time I tell him he should get the system upgraded !)
Does anybody have any comments on mixing refrigerants?
I've got another system which is R502 charged but needs a "top up".... Could I top it up with R408a ??..
If I did ...What would be the consequenses ? ...Will these gases mix and still perform.....or should I tell the customer he needs a reclaim and recharge (retrofit) ?
Quote:
Originally Posted by Brian_UK
Just normal freezer, chiller cold rooms
Says fitting them will save a compressor going down.
But, low back pressures are just fine........dont need controlling
Don't let Dez see this Marc :eek:Quote:
We're looking for a mini-split installation engineer £22K to £26K per annum...
http://www.fridgetech.com/employment/
Crank case pressure regulators are normally fitted to condensing unit systems with 1 or multiple evap's and electric defrost (hot or cool gas defrost would mean that the compressor is running and therefore the pressure would not increase to an unacceptable level). This is purely to limit the pressure in the compressor crankcase on start up. Once the pressures have equilised there should be NO pressure drop accross the valve. Another way of preventing excessive crankcase pressues is to fit a MOP Tex.
Quote:
Originally Posted by frank
Frank,
Marc is the only guy around here who will get away with murder on this forum!!!
Dont follow his cue...............Youll get nailed!!!
;)
Aiyub
As a rule Crankcase valves should be fitted to low temperature units, where you have high suction pressures after a defrost, or high loads on start up this saves the compressor on high loads after defrost, usually the average freezer will have a suction pressure of 80-90 psi after defrost if you are not using a fan delay on the evaperator, this added load on the compressor causes higher than normal head pressures, and burning of both valves and windings, the correct approach is either a Maximum Operating Pressure TEV or a CPRV, with a fan delay on the evaperator either set to temperature or on a timer.
I hope that this info helps, but yes CPR valves do help save compressors when installed correctly
Burning valves and windings ???:confused: :eek:Quote:
Originally Posted by andre_fridge
That's what I meantQuote:
Originally Posted by Marc O'Brien
You,.. asking me why?Quote:
I give up, Peter, tell me then, why not use a MOP?
Apparently Peter, Mark is confused again, poor soul, You need to simplify your posts or write them in Africana :D :D anyway Mark for your education:)Quote:
Originally Posted by Marc O'Brien
MOP is normally used to prevent system flooding, compressor overload, or to limit flow at startup under lightly loaded conditions. In some ways it is appropriate to compare the MOP of a TEV to the function of the traditional crankcase pressure-regulating valve, or the mechanical pressure-limiting expansion valve elements therefor a thermostatic charge with the MOP feature causes the TEV to appear to close above a predetermined evaporator pressure. This limits the maximum evaporator pressure at which the system can operate.
Edited.
Satisfied?
Don't like word games.
Well, why then not install a MOP TEV?
We fit KVL's (CPR's) to med low temp freezers only as back up protection for the compressor. We set them at 10% lower than FLA.:)Quote:
Originally Posted by chillyhamster
Does a MOP perform the same funtion as a KVP?:)Quote:
Originally Posted by wambat
Hi Peter,Quote:
Originally Posted by Peter_1
When using a KVL and a expansion valve without MOP you will have instantly the full capacity on your evaporator available (after a defrost , ...). Where as if you use a TEV with MOP you'll have to wait untill the pressure at the evaporator outlet drops untill the MOP level is reached (or even a few degrees lower) before the expansion valve opens fully. So your pulldown time will be quicker with a KVL . (Less temperature fluctuactions on the products, ...).
But TEX with MOP also has it's advantages (no extra cost, no extra pressure drop in suction line, ...)
BR.
Bruno
You're right Marc. On the compressor side there will be little or no difference. But what I ment was that the TEV will feed the evaporator completely with liquid as soon as the solenoid valve opens (without any limitations, only controlled by the superheat). The TEV with MOP will not open instantly (and fully) when the solenoid opens. If it's an MOP at -20°C. The TEV won't be open fully before the To is lower then about -25°C. So there is a difference in 'efficiency' on the evaporator side.
(When I ment pull down time, I ment 'air side' and not the 'suction pressure side'. I don't know if I use the correct English terminology).
Bruno
You know propably that I know how it's all working and when to use what item BESCIE.Quote:
Originally Posted by BESC5240
It's only that I don't like brain teasers, word trivia games and psychological games/speeches in a technical forum.
And I don't wanna spend the litlle spare time I have on such a trifles which has nothing to do with my view of this RE forum.
Well said Peter, butI dought whether the message will get through:confused:Quote:
Originally Posted by Peter_1
Theoretically seen yes, practical...no, not at all.Quote:
Originally Posted by Marc O'Brien
And a compressor will run practcial, not theoretical.
Say you have a compressor with a max evaporating temperature of -10°C at 45°C condensing (a Bitzer Octagon) for example. Cooling capacity at -10° compared at -25°C is almost double.
Case 1 : Normal TEV and a KVL mounted and regulated for full compressor load or evaporating at -10°C.
After a defrost or at start-up at warmer conditions, compressor will evaporate at -10°C at full capacity and the heat present in the coil after defrost will be released very fast because we have double capacity as compared to normal freezing (-25°C) condition.
TEV will feed evaporator maximum as far as allowed by minimum superheat, so a wetted evaporator.
Case 2: MOP -25°C installed no KVL. After a defrost or at start-up at warmer conditions, compressor will evaporate at -25°C at half the capacity (compared to case 1) and the heat after defrost will be released in half the time.
This because the injection in the evaporator is temporarily reduced by the MOP till evaporating temperature match the max evaporating temperature of compressor.
The KVL limits it to a the max allowable compressor value , chosen by the technician and adapted to the connected compressor where a MOP limits it to a by the manufacturer preset value, no matter how high the compressor can evaporate.
A system with a TEV with a KVL will pull down much faster copared to MOP/no KVL due to the higher evaporating temperature and a better filled evaporator and it will certainly run with a better COP during pull-down.
So there is for me a great difference and I agree with BESC5240's statement.
If you already stated this in a previous post, then it was not clear enough for me and then probably also for some other readers.
Quote:
Originally Posted by wambat
I second that..........
and......
I stopped responding to idiots a long time ago
1. Blantantly biased...???:confused: That's your point of view of the situation or my explanation, I have mine.Quote:
Originally Posted by Marc O'Brien
2. A MOP with a higher then KVL setting??? Why on earth should someone do this, unless he don't know what he's doing? This is certainly a theoretical assumption, never used in practic.
A MOP at -10°C where the compressor has a max operating evaporating temperature of -20°C, set by the KVL. 100 x :confused:
Why then use a MOP anyway with a compressor connected to an evaporator? It's a MOP without or no-MOP with a KVL (1 compt/1 evap)
3. Sure, I'm reading his posts, why shouldn't I, we were colleagues for some years.
Is there something wrong with it, otherwise I will stop reading his posts if that upsets you. :(
I hope that weather improves quick a litlle bit and temperature rises because with the falling of the leaves .....
Have to work now, haven't all the time right now:D :D :D .
Aiyub, what happened with your post?
No, it doesn't perform the same.Quote:
Originally Posted by Marc O'Brien
A MOP limits evaporating pressure to a preset value, not adjustable where a KVL limts excessive crankcase to an adjustable pressure.
MOP limits flow out of the evaporator where KVL limits flow into to the compressor, so just the opposite.
If for some reason, crankcase pressure can rise further - for example when working with a reduced HP - then you can't use this benefit with a MOP but you can re-adjust with a KVL.
It performs completely different after a defrost where a KVL let through max mass flow and a MOP throttles to the set value.
A MOP with a higher then a KVL setting is not done, it's only a theoretical ...let me say .. a brainteaser.
Don't get your message. Did you mean, pretend with my last post or in the past?Quote:
Peter, you're a lot more intelligent than you're pretending to be. Cut it out!
Anyway, i have slept as well as every evening whatever you wanted to say.µ
a cpr valve is designed to regulate the load on a compressor. it is used in applications where (1) you do not have a txv with a low mop, and (2) to keep the amp draw down in pulldown of a hot box or when you have hot gas defrost. it is only used to keep the compressor from being overloaded.
As the capacity of refrigeration compressor varies with the system compression ratio so does the power required to drive it. As the suction pressure reduces so does the power required – however this is not in direct proportion (see manufacturers catalogues)
To save costs, manufacturers match motors to suit different applications, say Low, Medium or High Temp /air conditioning ranges.
This means that Low Temp motor /compressor units may not have sufficient power to suit operation when operating with high back pressures during ‘pull down’ or hot gas defrost.
If the overload is of relative short duration the motor would possible be OK. If NOT an automatic ‘crank case regulating valve’ is one solution. (I can remember having to slowly opening the suction vale on large compressors during start-up to prevent the motor overloading and the ‘rattle’ of the compressor sprung heads if opened too quickly so as to allow liquid to came flooding back from flooded type evaporators).
The fitting of a ‘crank case regulating valve’ is only for this purpose and is not intended as a means of capacity control. It should be set to be fully open at or slightly higher than design suction pressure. If selected correctly – with a low pressure drop at normal design conditions it should have little effect on system capacity.
Larger air conditioning water chillers can have the same problems when starting after a prolonged off period when the chilled water temperature can rise to that of the ambient. In these cases the control system modulates the compressor capacity controls
in response to the motor lull load power.
These days electronic expansion valves can be configured to provide the necessary protection.
Hey im new here but might help.
They are neccesary when you are working with compressors that are designed for low temprature refrigeration. They limit the back pressure when the compressor starts up and the room is at a high temprature, this prevents the compressor amperage from exceeding its rating and the head pressure from screaming. If the system is using hot gas bypass they are also used to keep the back pressure low during bypass. I personally would fit one to a freezer room just to prevent nuisance overload trips if the room gets switched off and restarted later.
Use a CPR on Low temp system is best to reduce start-up pressures.Regarding the R502 to 408 question - Go for it ,topping up with 408 has been done and is still operating like it still has 502 in it . The great thing about this is we are not recliaming and then having a bottle of 502 that we dont know what to do with apart from take back to the wholesalers and get $5 kg for it. When they charge a lot more than that for the 408 . :DQuote:
Originally Posted by Richard Towns