Bypassing a smv valve on carrier reefer

[hzu]

On a recent trip i had this problem. I was on a ship and had a carrier reefer that had a bad smv valve ( would only open 27%). I didn't have a spare on board so I took the valve apart and removed the piston as the manual said. Well while trying to adjust the temp with the suction service valve i encountered the following problem. The discharge pressure would go so high that it kept opening high pressure cutout switch. I had the suction valve almost closed then the pressure would go almost to the cutout limit and then back on and of while the temp would go down only during the period when the discharge pressure was going from high to low while average temp was going slowly up. I noticed that the quench valve kept closing and opening all the time. Now i always thought that when the smv is fully open the quench valve is suppose to remain shut. I keep wondering what did i do wrong and what was the problem.

[DaButcher]

Sounds like something besides a bad SMV. If it would open at all they usually work. % is controlled by lots of factors, if for instance the head pressure was high then the micro would only allow partial opening of the SMV. I have successfully "gutted" the SMV on other wise good refrigeration systems.

You may have had better luck if you would have controlled suction pressure by closing off the king valve instead of the suction service valve.

[hzu]

I'm sure it was a bad SMV cause it failed pre-trip and it wouldn't open past 27% when i set the temp way down. I wonder if it was air in the system cause i didn't bleed the system after I put the gutted SMV back? Alsow, I don't understand why the quench valve kept opening. isn't it suppose to be closed when the SMV is open all the way?

[DaButcher]

The quench valve opens when compressor discharge temp gets high enough

[abbsnowman]

Couple things here, what kind of unit is this? Sea going container?
Sounds to me that you have an issue with something other than the valve. If you are saying that you are closing the suction service valve and still getting high head, is the discharge check valve having issue? Is there a condenser shut off valve that is not opening all the way? Maybe some non condensables? Need more info...

[Grizzly]

Hi Guys, Please excuse my ignorance.
What's a "quench valve"
It's not a term that's used on this side of the pond.
Cheers Grizzly

[Reeferman27]

The suction modulation valve, SMV, is there to give capacity control during chill operation and as a compressor current limiting device in all operations. The quench valve opens on high discharge temps. to cool the compressor motor windings. You you need to give the model of the container/controller and the configuration settings.

[hzu]

Yes it's a sea going box. I'm off the ship now so I don't have the box in front of me all i know is that it's a micro link 3 carrier reefer, one of the newer units. The suction service valve had to be ALMOST closed for the high pressure switch not to trip. It never happened to me before so I'm really curious what was it. I work on container ships and want to know how to avoid this problem in the future. Thank's guys for your help.

[hzu]

It was a 26 F box. and all i could do is to bring the temp to 31 F. In retrospect i think that when i put the gutted SMV back I should've purged the air that was in the suction line. I think that what messed things up. What do you think?

[Grizzly]

The suction modulation valve, SMV, is there to give capacity control during chill operation and as a compressor current limiting device in all operations. The quench valve opens on high discharge temps. to cool the compressor motor windings. You you need to give the model of the container/controller and the configuration settings.

Thanks for the explanation Referman!
Is the quench valve fed by liquid or Vapour?
Thanks Grizzly

[Reeferman27]

The quench valve should be liquid fed. It usually is used when the SMV is closed during capacity control, and not enough ref. getting back to cool comp.

[Reeferman27]

The quench valve should be liquid fed. It usually is used when the SMV is closed during capacity control, and not enough ref. getting back to cool comp.

Not allowed to edit??

Should have mentioned that this quench valve is very similar to a TEV, using the suction pipe temp. to site the bulb.
file:///C:/DOCUME%7E1/ANDYAN%7E1.000/LOCALS%7E1/Temp/moz-screenshot.pngThis is fitted to the units with 06D recip. comps NOT the scroll.

[hzu]

Not allowed to edit??

Should have mentioned that this quench valve is very similar to a TEV, using the suction pipe temp. to site the bulb.
file:///C:/DOCUME%7E1/ANDYAN%7E1.000/LOCALS%7E1/Temp/moz-screenshot.pngThis is fitted to the units with 06D recip. comps NOT the scroll.
I've seen it on some older TKs with scroll comps as well. I can't remember the model N.

[adacus1]

Although you don't list the model number of the unit from your descrtiption the most likely model seems to be a 69NT40-541 Thinline ML3 with recip compressor.

Was the condition you describe for after the SMV piston was removed, similar to that which was happening prior to removing the piston? In other words initially the unit wouldnt cool, had high head pressure and the SMV was almost closed. While after removing the piston the unit wouldnt cool, had high head pressure and the suction service valve had to be almost closed before the head pressure came down under control. If this is the case then the SMV was working correctly and was attempting to control the head pressure as described below. The most likely real cause was failure of the discharge pressure regulator. Normally this is fully open above 70psi, in cold ambients when the discharge pressure tries to fall below 70psi the regulator closes to bring the head pressure up. If the regulator valve fails it can slowly close raising the head pressure until the micro sees head pressure approaching high pressure cut out and closes the SMV to prevent a compressor stop.

The SMV serves three functions - Primary of which is to reduce capacity during perishable operation and control the unit to setpoint. Second function is to reduce system current draw if the current limit is exceeded and third to control the discharge pressure in the event the High Pressure Switch limit is reached.

[bruisermac]

as long as the unit has 5147 or greater software, a ML3 controller and SMV you can eliminate the DPR if necessary on any recip unit out there.