I want to build a compressor

[Seadog]

its the one that has the wound copper pipe going in to it from the valves ,

That's what I thought you were referring to. How does it function?

 

[brightspark]

That's what I thought you were referring to. How does it function?

when the pressure builds up at the bottom theres a type of piston inside and its spring loaded it can be adjusted for diffrent pressures . when it lifts it opens the port feeding the valves and holds them open till the pressure drops then closes leaving the valves free to compress

 

[mtt.tr]

So to recap - you need to fill the tank full with water, then pressurise it to 1.5 times the working pressure.
The working pressure is the pressure your relief valve, fitted to the tank, will lift (so you need to get one of those).
You will need an air pressure switch with adjustable differential between start and stop.
You will need a solenoid valve that gets fed from the normally open contact in the presdure switch, so that it dumps the air in the line between the compressor and a non return before the tank (unless there is a mechanical one built into the compressor).

I'm sure someone will tell me I'm wrong, but those are the bits I'd expect to see.
Edit to add, I've used a fridge compressor to pressure test before now, so long as the tank is full of water the energy release factor will be low (should it fail).

Only part if change is do for a self unloading switch

 

[Seadog]

when the pressure builds up at the bottom theres a type of piston inside and its spring loaded it can be adjusted for diffrent pressures . when it lifts it opens the port feeding the valves and holds them open till the pressure drops then closes leaving the valves free to compress

But surely that means that the pumpcontinues to run. Where's the pressure switch?

 

[brightspark]

But surely that means that the pumpcontinues to run. Where's the pressure switch?

yes the pump continues to run along with the motor but it stops the valves from closing and compressing when up to pressure and just cycles the air through the pump doing nothing

 

[brightspark]

heres a picture of another unloader valve that operates the decompressors on the valves at full pressure the small feed pipe at the bottom goes to the tank wherever it was https://www.mig-welding.co.uk/forum/threads/old-broom-and-wade-compressor-help.52207/

 

[Seadog]

Inefficient with the cost of electricity these days.

 

[Olderisbetter]

Nice looking old pump

 

[brightspark]

Inefficient with the cost of electricity these days.

yep best ignoring it and fit the electrical pressure switch but there good if you are running the pump of a diesel or petrol engine i had one on my 90cfm v twin run off a twin lister diesel engine for shotblasting

 

[minimutly]

You missed a non-return valve, but I'm pretty sure i can see one in the pictures. I can't see a mechanical unloader, neither can I see a pressure switch.

"he line between the compressor and a non return before the tank"

 

[minimutly]

Only part if change is do for a self unloading switch

Drunk this early @mtt.tr ?
You should try Welsh, I might understand that...
Edit to add - the only thing I think you're saying is to add an unloading switch? But that would need to mechanically lift valves etc? Wouldn't it?

 

[mtt.tr]

Drunk this early @mtt.tr ?
You should try Welsh, I might understand that...
Edit to add - the only thing I think you're saying is to add an unloading switch? But that would need to mechanically lift valves etc? Wouldn't it?

Some pressure switches have an unload valve built In. Only really on small compressors mind

 

[brightspark]

Some pressure switches have an unload valve built In. Only really on small compressors mind

general up to 14 or 18 cfm

 

[mtt.tr]

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This type

 

[minimutly]

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Got one of them on my piddly compressor. It farts a bit on startup sometimes.

 

[brightspark]

Got one of them on my piddly compressor. It farts a bit on startup sometimes.

i use my cheapo switch to operate a separate contactor to operate motor .the ones in the pressure switch arent up to much