Compressor valves and motors

[VW]

Been mix and matching compressor parts and have a couple of questions.

Basically, I have a very noisy 1.5hp sip compressor.
I also have a very quiet old hydrovane.
This one


The hydrovane has no receiver and is designed to run constant. I thought it may work better for me with a receiver So I took the sip apart and have created a hybrid.

It works well. I turned the pressure switch down to match the hydrovane 70psi maximum. All good.
But the sip stuff has 3 valves. The one way on the tank, a safety valve, and the one below.

It's this one I'm unsure about. It stays open untill the receiver has 20psi. Why?
Then, when it reaches full pressure and switches off the compressor it vents the compressor down to 0psi while leaving the tank at 70psi.
That's all well and good but as the hydrovane doesn't create instant pressure as well as the old sip pump it takes quite a while to make the 20psi to shut this valve.
I was going to taken it apart and see if I can get it to shut at a lower psi but figured I'd find out what it's even for before I mess with it.
Once the hydrovane switches off it vents itself down to 0psi anyway so I'm wondering if i can just take this valve out?

Secondly, the old sip motor. Is this really a 1.5hp motor? It looks a little small for 1.5hp.


I'm asking as I have this old grinder which I was going to set up as a polisher, but it only has a 1/4hp motor.
I was thinking of stripping/cutting the pump stuff off this and rigging it up to this grinder.



Suitable casing would be added.

Any thoughts?

[VW]

The only use for the valve I can think of is so the pump isn't starting against any compression.
The hydrovane doesn't seem to care.

[colnerov]

Hi, Yes that valve in venting the line from the compressor to the receiver to as you say make it easier for the pump when it restarts. It's sensing pressure from the pump to close its exhaust port and has a non return valve to stop the receiver exhausting back out again that way. If all that makes sense.

Colin

[VW]

I have took it off and blanked the hole. It works much better now. The hydrovane is happy to start while under pressure.

Only down side is removing this seems to make the one way valve vibrate a little annoyingly. Not sure why. It didn't do It when the valve was shut, which is the same as having no valve at all.

The only slight annoyance with the system now is the pressure gap on the power shut off switch. There is a 2 bar gap between off and back on. That's fine of your running the receiver at 120psi, but running it at 70psi means it drops to 40psi before kicking back in. Would be nice to be able to adjust start and stop points. On at 60psi, off at 70 would be nice.
I don't know if pressure switches can be had like that though.

[VW]

A little reading tells me I want a switch with adjustable differential.
I also see you want a minimum of 1 bar differential, which is fine for me.
I wonder if I can modify the original to have less differential.

[jimi]

Sept 8, 2021 15:39:39 GMT VW said:

The only use for the valve I can think of is so the pump isn't starting against any compression.
The hydrovane doesn't seem to care.

As already stated by colnerov (and as you correctly surmised) it's for pressure unloading, designed to let the compressor start off load and get up to speed before loading, very common on 3 phase compressor's with star/delta starters.
Adjustable differential pressure switches are pretty common. You can sometimes adjust the differential on a fixed differential switch, but very hit/miss to do and they tend not to be very reliable after they have been messed with.

[VW]

I added differential adjustment to my pressure switch. Seems it comes in both types. It's not made much difference though, sort of just let's you widen the differential a bit rather than reducing it.
So, I've bought another pressure switch that lets you set it down to 10psi differential.
However, it comes with another compressor! An incomplete, disassembled, compressor.
It has a 1hp motor too though so I can either get this new one running and see if it's too loud (the whole reason for the little hydrovane in the first place), or use the switch and vertical receiver with the hydrovane and use the 1hp motor on the polisher.

[melle]

Sounds like you've found yourself a nice new hobby. I have six air compressors, two of which I've bought new, three of which I've rebuilt, and one that's waiting for a complete overhaul.

[VW]

Sept 12, 2021 21:43:53 GMT melle said:

Sounds like you've found yourself a nice new hobby. I have six air compressors, two of which I've bought new, three of which I've rebuilt, and one that's waiting for a complete overhaul.

Seems like it!
Just picked the new compressor up. I may be out of my depth 😂
New thread coming soon so I can work out what goes where!