Screw Compressor with Slide valve problems

[xtnoblex]

so here's a problem, or maybe it isn't a problem.
I have a flooded screw type NG compressor that was replaced with a refurb, and now the slide valve is more open (109% from 101% ) than previous and the loading is higher (84% from 71%) and it is also running on higher amps (119 amps from 108 amps). all this is based on a the old data that I have from the previous compressors. Does anyone have any ideas?

 

[bcs5274]

has pressures changed at all?

 

[zdas04]

The slide valve is a gate that covers or uncovers a series of ports. When the ports are uncovered (100%), further movement of the slide valve has no impact on anything. Fully open is fully open, going farther does not make it "opener".

If you are used to seeing the indicator greater than 100% and now it is even farther above 1000% I would expect that the indicator is just shifted a tiny bit.

Valves like a slide valve are extremely non-linear. Going from 10% to 20% will be a flow rate increase several times larger than going from 80% to 90%. In fact I consider any slide valve position over about 85% to be fully open. Machines with turn valves instead of slide valves are slightly more linear, but not a lot.

Were I you I would be more interested in why someone replaced a machine that always runs as unloaded as it can get with the same machine. The only capacity control technique that wastes more energy than a slide valve (or a turn valve) is a recirc bypass. Any way to slow the machine down, lower the suction pressure, or raise the discharge pressure?

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist