Piloted Unloader Valves

[bc30se]

Hello

I need two valves to control my air compressor.. this is my compressor thread so you know what it's all about: http://www.mig-welding.co.uk/forum/threads/airpol-a170-compressor-restoration.48978/#post-565368


It produces 100CFM. Originally, two piloted unloaders were used with the 3/4inch outlets... similar to the one here:

http://www.ebay.com/itm/Gas-Compres...567?pt=LH_DefaultDomain_0&hash=item2eb9eab5e7


It is (im) possible for my to buy original ones but again... 80bucks a piece... they are quite dear, aren't they?
Do you know anything cheaper that would serve my purpose? Perhaps somebody could offer a workable workaround or a second hand one? I wondered if I could use a brake pressure regulator from a truck (hisser) but they give no data as for the flow, but they are cheapo (20bucks new), the one like that (Wabco: 9753034740)

All I know is they are preset at 8.1 bar, and I even don't know about possible adjustment or flow... anyone can help?

 

[Rig Pig]

Lorry compressors are usually very small, I think your 100cfm would be more than they could flow! You could use solenoid operated valves driven from a pressure switch.

 

[bc30se]

Thanks


I was thinking about solenoids but they cost as much as original pneumatic ones, and if I were to buy.. I don't know.... pneumatic are simple and idiot-proof, there are repair kits for them.. cheap... the problem is I bought my compressor without them and as I said.. the price is horrible for both..

but, could you show me such a pressure switch?

 

[Rig Pig]

I was thinking of a standard small air compressor switch eg eBay item 141376233940, you may have to use a relay to flip NO to NC if there isn't a normally closed contact in the switch but the unit is cheap, it just depends on finding some cheap SOVS. Have a look on eBay, there may be something suitable on there.

 

[MattF]

Can't remember any of the specs for them, but would these be any good for the task?

http://www.burkert.com/COM/Products/Solenoid-valves/Neutral-gaseous-media/0340.html

I'm sure I have a couple of those knocking about in the workshop which I've never figured a use for personally.

 

[bc30se]

OK.... Factory used two pressure controlled unloader valves with the diameter of 3/4 inch, as I understand it, it must be enough to unload 100CFM, otherwise they wouldn't have installed them.

The newer versions of the compressors used two solenoid valves: ASCO E210D009 (3/4 as well) but these I would rather avoid because they are expensive, they need some power pressure switch, and I don't trust them...

 

[AndyStobbs]

The engine driven compressors I have seen (in tyre fitting vans etc) use a mechanical blow off valve. Like this one in Machine mart

https://www.machinemart.co.uk/shop/...-pressure-unloader?da=1&TC=SRC-unloader valve

 

[bc30se]

Yeah these are small...

Anyway, guys.. as for unloading, what is going to be more efficient way of unloading in your opinion? To relaase air from the discharge pipe? Or just to prevent compressor's suction by using a throttle body?

I see these are two possible solutions given by the manufacturers... and to my mind a throttle body is better.. is it?

 

[AndyStobbs]

Will vacuum-ing the inlet side affect your oil distribution within the compressor?
I recently over-hauled a Steinhoj compressor that had the option of holding the exhaust valves open and hence not allowing the unit to build pressure. That was a good design, could you add any sort of decompression assembly?

 

[Rig Pig]

It would be a very bad idea to choke the inlet air, the compressor will be working very hard pulling a vacuum and suck air & oil past the rings from the sump. The whole point of an unloader is to let the machine 'freewheel' when not required. If your demand is low - not calling for many on/off cycles per hour you may be better to use a conventional electric stop start on the motor.

 

[bc30se]

I am not sure if it is going to be that bad if it is used on Quincy compressors... Polish compressor WAN-AW uses such valve in air filter.

Here:
http://obrazki.elektroda.pl/4415588100_1329726292.jpg

There is a tube providing air to the valve that sits in the air filter element.. once it is activated the air delivery is cut..

If my demand were low, I wouldn't be asking these questions, the motor is 22kw, not possible to switch-kill it... it must work all the time...

 

[Rig Pig]

If your intending to run it hard I would set up the unloaders as the manufacture designed, not cheap but like the rest of the machine - built to last.

 

[bc30se]

hmm I don't seem to get the answers to my questions this time but OK..... I haven't said that I am going to use anything cheap... so sorry for my minding your suggestions..

 

[Rig Pig]

My point is that the machine wasn't built with an inlet restriction, it may work but it may cause damage to the pump in the long term?? You may get lucky on eBay finding a second hand set of unloader valves but this sort of kit is going to be unusual. Keep us posted on the compressor it's a beautiful machine.

 

[bc30se]

I am going to be given original unloader valves from a locomotive service station (the same as original)... but I still think about making additional throttle valves just after the airfilters to unload it better. I think I could use 1.9SDI throttle bodies (simple and robust) plus a pneumatic operated valve... this would get rid of the permament hiss while on the unload. I considered vacuum problems as well but again, the compressor has quite a big intake so there is a chance that the air will travel back and forth, still might check it out by blocking the inlet with a piece of metal sheet and seeing what it is going to look like...

I worked for quite a long time with the Quincy 325 with the unloader towers right on the intake valves, I know the WAN-AW as well and they are damn quiet when unloaded just because this is the intake that gets blocked. Wheares, I had a chance to hear mine... a bit of a nightmare... a neighbour teaser definitely, sounds quite similar to an old truck passing by..

PS.
"the compressor has quite a big intake so there is a chance that the air will travel back and forth,"

wrong thinking, no chance....

Perhaps measuring vacuum on the crankase while the intake is blocked???

 

[AndyStobbs]

It'll pull a full vacuum. I've got a cheap old air compressor here, with pathetic output of 80psi, I converted it for vacuuming A/C systems and even that pulls a -950mBar vacuum. It will implode thin pipework too...

 

[bc30se]

The compressor is lubricated by the oil pump, so the oil circulation is forced.... the easiest way to do it would be just to block it and allow it to run for 5 minutes, then 10, 20, 30 minutes and see how the situation looks in the heads, and how much oil it has sucked from the crankcase..

For the time I will concentrate my efforts on running her on the original setup... then depending on results I will put throttle bodies on..

 

[normspanners]

Just a thought, why not unload the delivery pipe back into the inlet, 1/ to save pulling a vacuum 2/ make it quieter, the air might get a little hot but if it is not being compressed, its normal cooling system should cope and the air being recirculated would stop the 'thum' 'thum' of the air in the inlet.?? 3/ would reduce the air filter being blocked early due to not drawing fresh air in all the time . 4/ therefore cheaper to run

 

[bc30se]

I managed to buy OEM unloader valves and a pressure regulator, see them in the compressor thread.

http://www.mig-welding.co.uk/forum/threads/airpol-a170-compressor-restoration.48978/#post-565368