oil presssure on reciprocating compressor

[faryuki]

Dear Sir,

I want your suggest regarding the oil pressure for ammonia compressor. Recently i used reciprocating MYCOM compressor and have delta oil pressure is 2.5 bar.

Why the delta oil presure is 2.5 bar. why not 2 or, perhaps 1.5 bar?

how about for the high stage and low stage, there is have a different oil pressure also?

Waiting for any advise

many thanks

[taz24]

Dear Sir,

I want your suggest regarding the oil pressure for ammonia compressor. Recently i used reciprocating MYCOM compressor and have delta oil pressure is 2.5 bar.

Why the delta oil presure is 2.5 bar. why not 2 or, perhaps 1.5 bar?

how about for the high stage and low stage, there is have a different oil pressure also?

Waiting for any advise

many thanks

Oil pressure needs to be enough to ensure that oil flows to the furthest point from the oil pump and totaly saturates the shaft seal (if open drive).

The pressure is set by the manufacturer.
There is no reason in theory why you can't have it at 0.5b above crank pressure.

But you need to alow for the inefficiency of the pump and the oil pressure switch. It is better for control to have the oil pressure somewhere near the 3b mark to ensure safe control.

taz.

[John Hunter]

The standard Mycom recip has oil pressure charged load/ unload servo pistons. The soloniods relief back to crankcase to unload . If oil pressure is too high the unload sequence can be considerably delayed or not at all. 250 kpa differenial on all duties is quite sufficient for all lubrication purposes. What is as important as the circulation pressure is the oil on temperature 45 to 50 C max for all duties.

[US Iceman]

An adequate oil pressure provides several important functions:

One is noted by John Hunter... You need sufficient oil pressure to operate the unloader mechanisms. Oil temperature is also important since high oil temperatures tend to reduce the viscosity of the oil. Low oil temperatures can allow the solubility of the oil/refrigerant to increase so you have to limit the minimum oil temperature also.

A second consideration is the pressure has to be sufficient to provide hydrodynamic support for the rotating parts. If the oil pressure is too low the rotating parts may make contact with each other.

A third consideration is the actual oil pressure required by the compressor. For example, if you need 2 bar (differential) of oil pressure for the compressor to perform acceptably, you also have pressure loss through external tubing, solenoids, and filters. The oil pump outlet pressure needs to be sufficiently higher enough to overcome the "net" oil pressure for the compressor plus the losses due to flow.

[Grizzly]

It would be advise able to follow up on all of the above. Everyone has valid points. Simply put no two manufacturers ususally speciy the same oil pressure / diff. pressure.
for instance Grasso recips (RC11) have an oil diff of 1.5 bar (21psi ) whereas Sabroe (cmo) specify 4 bar (60psi).
In fact when the oil pressure starts falling off its usually time to investigate why. Studying your site maintenace records helps. ie. if a periodic maintenance is due then it's likely to be down to "normal wear and tear".
If the failing pressure is out of sequence with a maintenance schedule then maybe something else has failed. If you get to know your recips dropping oil pressure is usually an advance form of warning!
Cheers Grizzly

[Peter_1]

The standard Mycom recip has oil pressure charged load/ unload servo pistons. The soloniods relief back to crankcase to unload . If oil pressure is too high the unload sequence can be considerably delayed or not at all. 250 kpa differenial on all duties is quite sufficient for all lubrication purposes. What is as important as the circulation pressure is the oil on temperature 45 to 50 C max for all duties.

Isn' its so that it need pressure to load instead of unload?
When the compressor starts up - no oil pressure - then all then the compressor starts unload because the oil presure isn't high enough to load the compressor.
Once it's running and the oil pressure is building up, all the load valves are pressurised and the compressor run full loaded.
The SV's are NO valves, anyhow, this is so with Grasso

[PaulZ]

Hi Peter
John Hunter is right about the solenoids opening to unload and the problem with delayed unloading or not unloading. Mycom and Hasegawa compressors energise the solenoids to unload, where as old CP compressors energise to load. The power for these solenoids is either held on or off until the compressor is running at full speed, done through the aux contacts on the line contactor. 250 to 300 kpa oil pressure is pretty normal oil pressure for most of the compressors we work on regardless of whether they are high stage, low stage or compound machines.
If the oil pressure is too high it can cause increased wear on some bearings in some compressors.
Paul

[RANGER1]

Mycom A+B series sense oil pressure at the end of oil circuit. Mycom recommend 2 bar oil pressure differential.At drive end oil pressure would be higher,as after oil passes through oil filter/oil cooler it entersdrive end thrust bearing into crank.B or WB have parallel line going upto non drive end to feed main bearing and also can enter crank.Extra oil carry over can be possible if OP to high.

[Andy]

It would be advise able to follow up on all of the above. Everyone has valid points. Simply put no two manufacturers ususally speciy the same oil pressure / diff. pressure.
for instance Grasso recips (RC11) have an oil diff of 1.5 bar (21psi ) whereas Sabroe (cmo) specify 4 bar (60psi).
In fact when the oil pressure starts falling off its usually time to investigate why. Studying your site maintenace records helps. ie. if a periodic maintenance is due then it's likely to be down to "normal wear and tear".
If the failing pressure is out of sequence with a maintenance schedule then maybe something else has failed. If you get to know your recips dropping oil pressure is usually an advance form of warning!
Cheers Grizzly

Hi

Grasso's have two oil pressures, one for lubrication and one for loading, the loading oil pressure can be up to 8bar above suction.
I always though they were a bit lite weight with a poor 1.5-2 bar pressure, until I found outhey had a separate higher pressure system for loading.

Kind Regards Andy

[hendry]

Dear Sir,

I want your suggest regarding the oil pressure for ammonia compressor. Recently i used reciprocating MYCOM compressor and have delta oil pressure is 2.5 bar.

Why the delta oil presure is 2.5 bar. why not 2 or, perhaps 1.5 bar?

how about for the high stage and low stage, there is have a different oil pressure also?

Waiting for any advise

many thanks

Faryuki,
mycom recip comp has a oil pressure regulator which u can adjust oil pressure at any level u want.

lee, malaysia