Liquid Pump Problems

[CanadianIce]

Hi Guys

I was working on a system that uses Viking liguid pumps ( LL 480 ) on one of thier LPRs and Cornell on the second one. The vessels have common suction and liquid make up. These vessels supply -30 F liquid to several plate freezers, an ice maker and a cold storage. The Cornell pumps have no issues at all, however the Viking pumps do.
When I arrived on site the complaint was, the Vikings had lower than normal pressure ( 20 psi rather than 40 psi ) and pressure would be lost when suction hit 3 psi. I found many of the hand expansion valves open too far so I adjusted them all. Set up capacity controls on compressors so the suction pulled down slowly. Checked the pump regulator, no issues there. Adjusted both pump clearances and got the pressure back up to 45 psi, but the pressure would still be lost at 3 psi. Pulled the pumps from the housing to check for oil but there wasn't any. The pumps are quite noisy so I suggested complete rebuid or replace. After 2 days the clearance needed to be adjusted again to keep the pressure up so I assumed the pumps were grinding themselves to pieces due to worn internal parts. The customer opted for the rebuild. New parts installed and pumps still loosing pressure when suction reaches 3 psi. Any thoughts or suggestions?

Thanks
CanadianIce