Maneurop discharge valve reed broken, undersized orifice?

Hello everyone,

Lately, I had replaced a Maneurop LTZ88 to an NTZ215. Refrigerant is R404a. Box temperature
needs to be at least -19C.

The problem with the LTZ88, was a broken suction valve reed, which we found when doing a pump down. The causes were a bad piping design, a CFC drier being used and there was no additional components such as oil seperator and suction line accumulator. One thing to note is the condensing unit was in a false ceiling with an ambient temp of 38C. There was an orifice no.04 which was there at that time.

We replaced the compressor, done the piping designs, change drier, flush, vacuum, etc. We replaced that orifice with a new no.04 The system worked but on an evaporating temperature of -33C and condensing temp of +48C. We got the manufacturer's documents stating that an orifice no.05 was intended so we told that off to the customer that we needed to change it, sadly the customer said as long as it is working no need to go ahead. After a month we were called in saying that the compressor is overloading and cutting on the HP and the compressor was boiling hot. We suggested that we change the orifice to no.05 as per manufacturer's documents.

That was done and we had better results as we had a ducting system to have a better air in at the condenser, which was giving us +42C condensing temp, about 4K of subcooling, evaporating -25C and superheat of 8K.

After a few days the same problem occurred, cutting on the HP switch and the compressor is still boiling hot. We adjusted the pressure switch a bit higher up to 26bar normally set up at 23bars.

Only a few days ago, we had a call that the same was occurring. So we used the gauges and monitored the system. When the suction line temperature was going down to about +5C (box temp was +19 to +20C), the LP gauge started to rise up to RETARD on the gauge and the HP gauge fell down to +20C, my suction line was the same temperature as my discharge line, which led me to think that it has to be the discharge valve reed that is gone in one of the cylinders. Another thing to note that the oil was not too clear in the sight glass of the compressor.

My question could the undersized orifice and also the previous condensing temperature (+48C), have create slugging in the system? Was it normal that it took time to eventually damage the valve that badly?

Any information would be helpful.

An undersized orifice, would not cause slugging, but would cause, lower suction pressures, higher compression ratios, and high discharger superheat. You could have warped your head/valve plate or the valves

No, and undersized orifice valve causes a high SSH, surely not slugging.
In fact, at your specified working conditions the NTZ215 has a max limit of SSH of 10K, as per Maneurope envelope.
I assume the reed was damaged by excessive DGT caused by excessive SSH.

Alright, so the undersized orifice was the cause of it. That is one thing I wanted to clear myself off. Now my other concern is why after correcting the pipe design (yes it was the same as the manufacturer's) and all the others, that the discharge valve reed got damaged within a month and on the other hand the LTZ88 (older compressor) managed to last for at least 2 years (from what I heard there was always capacity issues with it), even with a bad piping design.

As far as I know both reeds are of the same materials.

by adding the suction accumulator you will of increased the compressor suction super heat (more surface area for the already superheated gas to heat further)
As NNN has said max superheat "AT" the compressor inlet is 10k(C), this not to be confused with the superheat at the expansion valve bulb at the evaporator

Quote:

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Originally Posted by mad fridgie

An undersized orifice, would not cause slugging, but would cause, lower suction pressures, higher compression ratios, and high discharger superheat. You could have warped your head/valve plate or the valves

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Just like the first time we installed the compressor. -33C on suction and +48C on discharge.

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Originally Posted by Ashwin123

Just like the first time we installed the compressor. -33C on suction and +48C on discharge.

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Correct! Did you see frost on your compressor suction service valve?

Quote:

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Originally Posted by mad fridgie

by adding the suction accumulator you will of increased the compressor suction super heat (more surface area for the already superheated gas to heat further)
As NNN has said max superheat "AT" the compressor inlet is 10k(C), this not to be confused with the superheat at the expansion valve bulb at the evaporator

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Sadly the customer didn't agree to put either a suction line accumulator or oil seperator (pennywise but the foolish) also to note there was a restriction in the space and the customer never agreed to move out the unit. Yes, the discharge was quite high about +85C at that time.

Quote:

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Originally Posted by mad fridgie

Correct! Did you see frost on your compressor suction service valve?

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Not that I remembered seeing any frost on the suction line valve, to note that the ambient temperature is quite high there and there is almost no ventilation or whatsoever at that time.

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Originally Posted by Ashwin123

Not that I remembered seeing any frost on the suction line valve, to note that the ambient temperature is quite high there and there is almost no ventilation or whatsoever at that time.

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I thought you had made modifications (sorry for not understanding what you had done)
You need to either adhust the expansion valve to reduce evap superheat to reduce suction superheat or add liquid to your suction, you should be seeing frost on the suction service valve.

Quote:

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Originally Posted by mad fridgie

I thought you had made modifications (sorry for not understanding what you had done)
You need to either adhust the expansion valve to reduce evap superheat to reduce suction superheat or add liquid to your suction, you should be seeing frost on the suction service valve.

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At the time of the replacement we had not touched the orifice only replaced it with the same but new one (the other one had oil and the oil was trapped in the condenser and evaporator due to bad piping design). We did not have the manufacturer's documents yet and never thought that someone would be smart enough to put an undersized one there.

One thing I noticed is after replacing orifice no.04 to no.05 and figuring out the discharge valve reed has been damaged. The outlet of the expansion valve and distributors were frosted. My expansion valve is a MOP valve by the way. I note that my expansion valve head was lower in temperature than the bulb temp, which is so far so good.

Quote:

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Originally Posted by Ashwin123

Alright, so the undersized orifice was the cause of it. That is one thing I wanted to clear myself off. Now my other concern is why after correcting the pipe design (yes it was the same as the manufacturer's) and all the others, that the discharge valve reed got damaged within a month and on the other hand the LTZ88 (older compressor) managed to last for at least 2 years (from what I heard there was always capacity issues with it), even with a bad piping design.

As far as I know both reeds are of the same materials.

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Can someone answer to that question?

is the unit on a mop tev cpr or any form of regulation please advise:):)

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Originally Posted by charlie patt

is the unit on a mop tev cpr or any form of regulation please advise:):)

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There is only a MOP 30 expansion valve and nothing else. No CPR would be used because of the existing MOP valve.

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Originally Posted by Ashwin123

One thing to note is the condensing unit was in a false ceiling with an ambient temp of 38C.

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You are pumping heat into an enclosed space? That's insane.

gary is spot on if it has a mop and mag valve and the orifice is speced correctley then heat is the fault

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Originally Posted by Gary

You are pumping heat into an enclosed space? That's insane.

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This is what the hotel guys made the previous contractor do, and when we asked to move it out, they say "its not in the budget to do and its not in their control". Sadly it is a fact!

Alright, so the undersized orifice was the cause of it. That is one thing I wanted to clear myself off. Now my other concern is why after correcting the pipe design (yes it was the same as the manufacturer's) and all the others, that the discharge valve reed got damaged within a month and on the other hand the LTZ88 (older compressor) managed to last for at least 2 years (from what I heard there was always capacity issues with it), even with a bad piping design.

As far as I know both reeds are of the same materials.

No one still gave me a clear idea about the above statement. The setup has always been the same, that is being in the false ceiling. Why the previous compressor LTZ88 "managed to work for 2years" even with an undersized orifice, bad piping and a damaged suction valve (I would consider that the temperature went down to -19C) and the new NTZ215 with the right orifice, piping according to manufacturer's specs have come to a damaged discharge valve?

There are other units again in that bloody false ceiling and all seem to be working according to the guy. But I must admit that only where that unit is there was no air circulation at that time. But only this month, we managed to do more or less something about it, making it go down to 36.5C.

The undersized orifice was not the cause.

The better the system works, the faster it pumps heat into that false ceiling.

You need to pump cool air into that space and pump hot air out of that space. The false ceiling needs maximum ventilation.

the heat is the leading issue but did you check the tev set up these maneuropes are ment to be double skin but they will smash up as quick as any thing when liquid is involved is the mop set up correctley reset hp pressure switches save eqipment to high bad news on hp to low on lp and pulling a vac just as bad the biggest fault i have had with breaking plates is liquid return

High head pressure can cause hunting and slugging. When the box is down to temperature (low load) the TXV calls for a little liquid and the high pressure delivers a lot of liquid.

The larger orifice just makes it worse, allowing a larger slug.

Because of the head pressure problem, it would have been better to go to a smaller orifice, not larger.

It all comes back to pumping heat into an enclosed space. The electric consumption must be enormous pumping against all of that pressure... not to mention the reduced lifespan of the equipment.

What happens when all of the equipment in that enclosed space is running at the same time? How high would you imagine the head pressure to go when that happens? They are all heating each other.

It's just insane.

as yes gary but a customers clouded vision can sometimes be hard work you can advise and guide a customer but the first call on this one is the heat as you have said .... move the unitor give it fresh air,, give it fresh air,, water cooled condensor or a heat exchanger or remote the condensor

Did you change the contactor when you fitted the new compressor?
Is it single or three phase?
Is it on pumpdown cut out?

Quote:

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Originally Posted by Gary

High head pressure can cause hunting and slugging. When the box is down to temperature (low load) the TXV calls for a little liquid and the high pressure delivers a lot of liquid.

The larger orifice just makes it worse, allowing a larger slug.

Because of the head pressure problem, it would have been better to go to a smaller orifice, not larger.

It all comes back to pumping heat into an enclosed space. The electric consumption must be enormous pumping against all of that pressure... not to mention the reduced lifespan of the equipment.

What happens when all of the equipment in that enclosed space is running at the same time? How high would you imagine the head pressure to go when that happens? They are all heating each other.

It's just insane.

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The unit picks up more amp than usual on start up. We did actually tell the customer that we can go through the other methods of cooling, but it was just echoes in a hall.

When there was the smaller orifice (i.e. no.04, there was low evaporating temp -33C and high condensing temp +48C).

Because of the abnormal pressure we obtained after replacement of the compressor, we simulated the system on a program that eventually led to orifice no.05 as the best choice and also the manufacturer's documents mentioned that it is a no.05. We warned the customer that this should be changed but its only when the compressor started overloading (after a month) that, he said to go ahead and change it. Could that mean that the smaller orifice has damaged the discharge valve already by that time? As all I did on the 2nd call was increase the HP switch and it went down as usual (i.e. -19C, and had an HP of +46C and LP of -25C). Then on the 3rd call, same problem, HP cutting out and compressor boiling, I monitored the system and finally found out with my LP climbing up to RETARD and my HP going down to +20C, it had to be the discharge valve.

The other units seem to have an exhaust at the condenser air out and a discharge at the condenser air in from ducting systems. The problem that I noticed with this unit is that it is throwing the air out of the condenser into the monoblock (where the compressor is) and there was no exhaust duct at that time.

The compressor is a 3ph compressor and no contactor was changed as when we tested them, they were still in condition except one had a buzz.

Quote:

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Originally Posted by charlie patt

the heat is the leading issue but did you check the tev set up these maneuropes are ment to be double skin but they will smash up as quick as any thing when liquid is involved is the mop set up correctley reset hp pressure switches save eqipment to high bad news on hp to low on lp and pulling a vac just as bad the biggest fault i have had with breaking plates is liquid return

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The TEV was set up correctly and I checked that the MOP was too by checking the temp of the expansion valve head and bulb. It works on a pump down system, regulation through LP. My HP was set on 23bars (since my condensing temp was on +48C on the first call).

Maybe it is a little confusing because of the chronological order, I will make it simpler.

System with LTZ88, with bad piping design, undersized orifice, oil trapped in the condenser, drier, evaporator, bad filter drier and high ambient temperature and no ventilation, last 2 years with ending results the suction valve gone.
V/S
System with NTZ215, with proper piping design, new filter drier, flushed, vacuumed and properly charged, with undersized orifice and high ambient temperature last only a month with ending results a damaged discharge valve?

I think that looks better? Right?

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Originally Posted by Ashwin123

When there was the smaller orifice (i.e. no.04, there was low evaporating temp -33C and high condensing temp +48C).

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The evaporating and condensing temps have little to do with orifice size and everything to do with effective surface area and temperature and volume of air flowing through the coils. Without knowing the temperatures of the air entering the coils, the evaporating and condensing temp tell us nothing useful.

Quote:

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Originally Posted by Gary

The evaporating and condensing temps have little to do with orifice size and everything to do with effective surface area and temperature and volume of air flowing through the coils. Without knowing the temperatures of the air entering the coils, the evaporating and condensing temp tell us nothing useful.

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The air in at the condenser was previously +39C and air out about 45C, the time we replaced the compressor. The box temp without any load was +18C but after the compressor was replaced it eventually went down to -19C quite easily.

Then again you are right Gary as I do not know what the air temp was when it was installed. There was only a discharge PVC duct that was hardly throwing out any air near the air in at the condenser at the time I was there.

So in your opinion, it is more on the hot air circulation than the orifice?

Quote:

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Originally Posted by Ashwin123

The air in at the condenser was previously +39C and air out about 45C, the time we replaced the compressor.

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If the air in was 39C and the air out was 45C, then how could the condensing temp possibly be 48C?

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Originally Posted by Gary

If the air in was 39C and the air out was 45C, then how could the condensing temp possibly be 48C?

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Sorry that is 55C not 45C, typo. There was no air exhaust at that time in the monoblock.

Quote:

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Originally Posted by Gary

High head pressure can cause hunting and slugging. When the box is down to temperature (low load) the TXV calls for a little liquid and the high pressure delivers a lot of liquid.

The larger orifice just makes it worse, allowing a larger slug.

Because of the head pressure problem, it would have been better to go to a smaller orifice, not larger.

It all comes back to pumping heat into an enclosed space. The electric consumption must be enormous pumping against all of that pressure... not to mention the reduced lifespan of the equipment.

What happens when all of the equipment in that enclosed space is running at the same time? How high would you imagine the head pressure to go when that happens? They are all heating each other.

It's just insane.

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I found something new today, this is actually the 3rd time in 2 years that a compressor has been changed on this unit. The first compressor had damaged pistons, broken reed valves, oil slugging, the second one broken suction reed valve and the 3rd one (the one I installed) a damaged discharge reed valve.

Then all that you stated, that it is pumping heat and the orifice problem. It all leads to the same problem, as long as the condensing unit is still locked up in that false ceiling.

There is one thing that is strange, the condenser's air out is in the monoblock while the air in is outside. Shouldn't that have been installed in the other way round?

Thanks a lot for enlightening me, all of these came very helpful and makes more sense.

Pumping air into an enclosed space is like blowing into a bottle. The flow stops. The air must be able to both enter and exit that space.

I'm wondering if the comp is going off on its internal thermal overload due to the high condensing temperatures, and when it resatarts it slugs and damages the valves.

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Originally Posted by monkey spanners

I'm wondering if the comp is going off on its internal thermal overload due to the high condensing temperatures, and when it resatarts it slugs and damages the valves.

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It was cutting off on the internal thermal overload and at times it would jump off the main circuit breaker.

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Originally Posted by Gary

Pumping air into an enclosed space is like blowing into a bottle. The flow stops. The air must be able to both enter and exit that space.

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Try to explain that to the "chief engineer" of that chain hotel. Those guys even removed the grill off the vents that was discharging cold air and also removed the vents from the exhaust. To make things better they placed the two outdoor 60000BTU outside of the air discharge duct. :rolleyes: