150lt SIP general plumbing advice

[Mattycoops43]

Hi all.

I am after a bit of general advice as to how a belt drive compressor is set up. I have had a small 25lt direct drive compressor for ages, but it was too small to drive anything useful to me. I recently got offered a 150lt SIP belt drive from a friend who does house clearances. It is old, has some surface rust where the paint has been damaged, but it cost me £50 and it works when turned on.

So, I need to service it, and check it for safety. My question is about the plumbing. The pressure switch had no off button so I put a new cover on it, now it is doing a couple of odd things, which I think may just be NRV not working, but it is so different from my previous one, I am not quite sure what valves should be doing what, for diagnosis purposes.

I have run it up to 80psi for purposes of testing it works. When you turn it off with the button, it pushes down on a valve that releases air from under the switch cover. it is also bleeding air back through the air intake. I know the NRV would cause the second thing, but would that also cause the air to leak from the pressure switch cover?

Then the other thing I noticed, is I ran it up and turned it off before it cut out, but then when I turned it back on it had reached the pressure where it would not start without losing more pressure, and it was now leaking air from the pressure switch when turned on. If you turned the switch off, it release air faster, but I could not stop air leaking from the switch.

I hope this makes sense. Bit difficult to describe when I am not sure of the terminology. I THINK i just need to get a new NRV, but it would be nice to know if there is something not working properly before i start taking it apart.

 

[rtbcomp]

Hi all.
...
but would that also cause the air to leak from the pressure switch cover?

...

Yes.

Try cleaning the NRV first, usually you can undo the end cap without taking it off the tank. Make sure the tank is empty first.

https://www.mig-welding.co.uk/forum/media/albums/compressors.206/?page=2

 

[Mattycoops43]

Yes.

Try cleaning the NRV first, usually you can undo the end cap without taking it off the tank. Make sure the tank is empty first.

https://www.mig-welding.co.uk/forum/media/albums/compressors.206/?page=2

Great Thank you.

Matt

 

[Mattycoops43]

Trying to identify it for parts.

 

[Mattycoops43]

Trying to find some wheels and the stub axle or bolts to hold them on.

 

[dannyp]

If it’s leaving out the pressure switch it’s the NRV. They can often be repaired ether rubber washer or the small springs worn out, mines had a few springs in the nrv now.

 

[Tifa]

If it's leaking air from the switch, it sounds as though the unloader valve in the switch is faulty.
Replace the switch (Buy the Italian one, not the cheap chinese copy...about £25 from ebay?) while you're at it, replace the pressure blow off safety valve too.
On an oldish compressor like yours, I'd suggest a blow off valve rated at 8 bar (115 psi 'ish' )

 

[Mattycoops43]

Great thanks. I had not done anything with it yet, been too busy. That sounds like a plan though.

 

[rtbcomp]

If it's leaking air from the switch, it sounds as though the unloader valve in the switch is faulty.
Replace the switch (Buy the Italian one, not the cheap chinese copy...about £25 from ebay?) while you're at it, replace the pressure blow off safety valve too.
On an oldish compressor like yours, I'd suggest a blow off valve rated at 8 bar (115 psi 'ish' )

If it leaks from the switch when the compressor is running it will be the unloading valve (or the bit in the switch that activates it)

If it leaks from the switch when the compressor has cut out (or you operate the red button) then it's the non-return valve.

The compressor should give a hiss (about 1 sec) when the compressor cuts out, if it doesn't then it's the unloading valve, the bit in the switch that activates it, blocked unloading pipe &c.

 

[Mattycoops43]

Thanks. It does both. As pressure builds there is a hiss from the switch, then if you hit the red button it doubles, so I think I'll check and change both. Also blow off valve and drain valve. I think I might as well change all of them for the cost. Does anyone have a link for a proper switch? I have bought a cheapie Chinese one in the past for a 25lt one and the market seems to be flooded with them.

 

[rtbcomp]

You need to sort the NRV as mentioned earlier. You'll probably find the unloading valve on a new switch will have a push-fit connector for a plastic unloading pipe, so make sure any new NRV has a compatible connector on it.

 

[Mattycoops43]

In all honesty, I will probably take the whole thing apart and just rebuild it checking as I go It's what I enjoy doing anyway.

I notice it had big end caps each end of the reservoir. Is there any issue taking these out to check inside and give it clean out?

 

[rtbcomp]

That would be a good idea, on mine I swapped them over because I wanted the outlet tap on the other end, that might be something to consider.

 

[Mattycoops43]

On mine the outlet is on the very end of the cylinder in the end cap.