pump out vs pump down

[tarcau mihai]

Hello guys!
Can anyone explain which is the difference between pump out and pump down?all what i know is that in both cases when the solenoid liquid valve will close ,the compressor is shutted down by the lp presostat...is it something else?
tks
Mihai

[Brian_UK]

Pump out systems tend to be used in ammonia systems and are better explained here....

http://www.process-cooling.com/CDA/A...00f932a8c0____

A pump down system is a one where on reaching design temperature the liquid line valve is closed and the refrigerant still in the evaporator and lines is pumped by the compressor into the condenser side. When the pressure is reduced to the pressure switch setting compressor will stop.

This system should prevent liquid slugging back to the compressor on restart amongst other benefits.

[Entropie]

My understanding of pump out and pump down is, that after a pump out cycle the compressor remains off until the thermostat is opening the liquid linesolenoid valve and enable the compressor to start. On a simple pump down, the compressor is allowed to do recycling pump downs whenever the suction pressure rises and a certain time has elapsed without run permission of the thermostat, just to pump down the system again with closed liquid line solenoid valve.

regards,
Entropie