Advantages of a pumpdown system for cooling tank

[kallileo]

Do you see any advantages of having pumpdown system on cooling unit with a MTZ72 (6HP) compressor for 2000lt water cooling tank?
I'm not talking about a remote unit as the cooling units is installed on the tank and the there is around 7kg of refrigerant in the system.
As far as I know the pumpdown system is used to prevent refrigerant migration to compressor and crankcase.

[Glenn Moore]

Hi Kallileo
The MTZ 72 compressor has a refrigerant charge limit of 5Kg which is the limit of charge that the compressor can safely have inside the compressor shell without entering into the compressors suction port. But your system with 7 Kg of refrigerant , if allowed to get into the compressor during the Off cycle could cause valve, piston and con rod damage due to excessive liquid charge.
So by using a pump down you are safeguarding the compressor from being damaged by liquid migration and also helping to protect your compressors warranty if applicable which could save you a lot of money and problems.

[kallileo]

Hi Glenn,

It seems that there is a small issue with system as the compressor turns on automatically for few seconds pretty often especially during summer probaly because of the sensivity of the low pressure switch which has a range of 0,3 - 2,2 bar.
Could I avoid these unwanted starts by replacing the low pressure switch?

[chemi-cool]

Hi Glenn,

It seems that there is a small issue with system as the compressor turns on automatically for few seconds pretty often especially during summer probaly because of the sensivity of the low pressure switch which has a range of 0,3 - 2,2 bar.
Could I avoid these unwanted starts by replacing the low pressure switch?

This will occur if compressor's suction valves are damaged or SV has internal leaking and has nothing to do with pumpdown.

[Glenn Moore]

Hi
Yes I would fit a different LP switch ie Danfoss, Ranco etc but set it with a larger differential setting ie 2 bar etc Often pump down machines pump down the system very quickly and leave a residual amount of liquid in the coil. This liquid quickly warms up and raises the suction pressure which remakes the LP switch and you get a restart. By increasing the differential the pressure will fail to reach the set point and the compressor cannot start, until the solenoid opens when duty is called for.