carrier screw chiller

[moideen]

Hay to all friends,

I have a doubt in screw chiller 30 GX-105 Ecologic. (Carrier)why does calculate the oil differential pressure which subtract the economizer pressure from Oil pressure.is it enough to subtract the oil pressure from discharge pressure?

[The Viking]

Now, please correct me if I'm wrong...

The oil pump is sucking oil from the sump or crankcase (depending on which side of the pond you're on), then pumping it around to various parts of the compressor.
The crankcase is generally at the same pressure as the suction line?

Hence, the true pressure generated by the oil-pump must be the pressure upstream of the oil-pump less the pressure in the crankcase (or suction line).

The discharge pressure (in this case) is generated by the screw itself and generally controlled by head-pressure controls and condensors. Thus it can vary, totally independent of the oil-pressure.

[Grizzly]

Now, please correct me if I'm wrong...

The oil pump is sucking oil from the sump or crankcase (depending on which side of the pond you're on), then pumping it around to various parts of the compressor.
The crankcase is generally at the same pressure as the suction line?

Hence, the true pressure generated by the oil-pump must be the pressure upstream of the oil-pump less the pressure in the crankcase (or suction line).

The discharge pressure (in this case) is generated by the screw itself and generally controlled by head-pressure controls and condensers. Thus it can vary, totally independent of the oil-pressure.

It's not often I get chance to correct an Engineer of your calibre Viking.
No offence meant but the above reference to the oil pressures being related to discharge pressure.

Is quite often highly relevant on a lot of Screw Compressors certainly the larger ones anyway.

I have a nice animated schematic showing the "workings" of a Screw liquid chiller unit.
Which I will try and send you. (It is quite a large file).

Basically the Oil Reservoir is below the comp with the
Discharge gas flow.
Travelling through coalescent filters which are open vented into the reservoir.
Which allows the oil recovered to drain back into the reservoir.
Therefor the reservoir ( and it's oil within) is at discharge temperature / pressure.

So similar to calculating a recips oil lube pressure by subtracting the suction pressure.
Some screw control strategies subtract the discharge pressure.
To arrive at what is the actual oil lube pressure.

Sadly I am not sure exactly what your question is Moideen.
Perhaps if you could rephrase it?
We may be able to help further.

Cheers Grizzly.

[Allrounder]

Think you will find most screws use the discharge pressure to "pump" the oil from the high pressure crankcase (carter) where it collects after going through the screw, If the discharge pressure does not rise above the set level after after a set time after start up the compressor will trip on oil pressure. Usually only HP is measured, LP is assumed.

[willow]

On this chiller you subtaract the oil pressure from the discharge pressure.With a new internal oil filter fitted expect about 60kpa pressure drop anything above 150kpa change filter. Compressor trips at about 220kpa