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Feeze
22-02-2005, 02:02 PM
Today I came across a Maneurop LTZ100 compressor which when the electrical power is disconnected from it, it appears to be running on. This is similar to that of a motor car engine with preignition problems. Has anyone else come across something similar?
My first thoughts are that it may have a broken conrod which continues to spin on the shaft after the compressor has stopped.
Regards,
Feeze

chemi-cool
22-02-2005, 03:07 PM
You may be right, such things can happen when liquid hits the valves.
You can easily tell as it hardly draws any currant and pressure does not change.

Chemi :)

Feeze
22-02-2005, 07:40 PM
Chemi,
There is pressure 20 psig suction 265 psig discharge 507 gas, 11amps/phase
400vac 3phase
I think that this compressor is a 4 cylinder and might have only broken 1 conrod.If I am not mistaken the pistons pump horizontally so the broken half of the conrod with the piston in it would just lay in the bore.
There does not seem to be any excessive vibration though and the compressor does pump down to 5 psig and settle down to 10 psig during defrost when the solenoid shuts.
One thing that bothers me is that the oil return pipe from the oil sep to the compressor is always cold whenever I check it.The oil in the oil sight glass is at a quarter while the compressor is running.

Feeze :)

chemi-cool
22-02-2005, 08:27 PM
If it "goes back" after stopping, a discharge valve could be faulty.

If the oil return pipe is cold and the oil level does not change, then all is well.
If it was cold and oil level in the compressor is getting too low, I would suspect a problem in the oil separator.

chemi :)

jsimon
22-02-2005, 08:42 PM
try to read the manufactures lable for the amp draw
carryout a pump down test into vac see if the valves are letting by
manurops in my experiance donot like vacuum sodo not run to deep or to long
it could be if you have liquid slugging back via the oil separator it could be forcing the pistons to keep spinning
rotary compressor do it all the time

Feeze
22-02-2005, 10:26 PM
Chemi,
How does one tell if it is nunning backwards?

jsimon,
label states 27amps max and 105amps locked rotor, it does not state if this is at 50 or 60hz
The label states further that the compressor is a 400volt60hz/ 400v50hz
My experience with these compressors is that they never run at 27amps. They typically seem to start running at about 15amps and then slowly drop as the fridge temperature drops, obviously other conditions also apply.
I found that if you used overloads of 27 amps you will not be giving the compressor much protection.
The internal overload usually cuts out before the external one does and you have to wait for hours for it to reset.

Please explain how liquid refrigerant returning through the oil seperator would force the pistons to keep on running on a recipricating compressor.Will head pressure not prevent the piston from continuing its compression stroke?

I have done a pump down test to -10 psig and the pressure rises to 5 psig within a minute and then hovers there.

Feeze :)

Feeze
23-02-2005, 07:00 AM
Thanks for the scientific explanation Mr O'Brien.

Feeze :)

chemi-cool
23-02-2005, 04:02 PM
Hi Feeze.

There is no "backward" in three phase hermetic compressors, they can turn in any direction.

If a discharge valve is broken, the high pressure gas, can push the cylinder back and it might turn the other way a little bit.

You can hear it if you are near the compressor and its quite.

Chemi :)

Feeze
23-02-2005, 05:15 PM
Marc,
Have you experienced the "shudder" on both old and new Maneurops?

Feeze

jsimon
23-02-2005, 05:54 PM
I think you need to deterimine if this is revelent b4 you spend to much time chasing your tail
If i remember correctly @ 50 Hz you will draw higher amps than @ 60hz
it may be possible that when the compressor shuts down that you are getting a high pressure rush from the oil return
causing the compressor to turn
the oil valve maybe closed due to the low suction pressure of R507
R 507 was a replacement for R502 or low temp use
what is the setup
regards jeff

Feeze
23-02-2005, 07:08 PM
Jeff,
There is no problem with the installation however we are just speculating about what I have observed and if anyone has observed something similar.The temperature of the 24 foot jumbo island freezer is fine and there are no other problems.
You are correct that current draw at 50hz is higher than at 60hz but I question the high pressure rush from the oil pressure return because that should cause the oil return pipe to be warm.I found it to be cold.
Furthermore I think that any high pressure returning to the sump will cause the crank to turn less than 1 revolution as the pistons have to work against head pressure. (can anyone back me up with this theory)
Could you please explain your comment "the oil valve may be closed due to the low suction pressure of R507"
Why would the low suction pressure cause the oil valve to remain closed? On the contrary I would imagine a high suction pressure would work against the oil pressure.
I open this to discussion.
Cheers,
Feeze

Feeze
23-02-2005, 08:13 PM
Marc,
Further on the subject of speculation I wonder if there was any "boom" in that pipe. Einstein sure looks freaked out. :D
I love your choice of avitars.
Thanks for the affirmation, I was beginning to think I was the only one that visualised the sequence.

Goedgaan,
Feeze

tonto
17-08-2005, 02:52 PM
I have known compressors to do this on room airconditioners when they are on there way out as in reeds being faulty, I would agree with chemi.....

paulcollis
17-08-2005, 11:14 PM
You would generaly find the machine would have to of had multiple broken conrods for the comp to run on as the friction of the other tree cylinders and there compresssion would slow the comp down immediately,i would say that it is more likely a discharge valve problem, this type of compressor runs a "discus" type valve arrangement, if there is no check valve in the discharge line when the comp cycles of high pressure gas will try to return from the condenser back to the comp, causing the cylender to pressurise and run in reverses for a short period of time, we have found that if this is the case the top of the compressor will start to run hot.