Snap-On HP12 Compressor Operation and Maintenance

[JonnyAlpha]

I would switch off the compressor & drain the receiver then remove and clean out the water drain valve, air and water should blast out when you open the valve with pressure in the tank to dump the produced water. See how much sludge and rust comes out, if there is a lot it would be worth removing the end plug from the tank and looking inside with a torch to see how much corrosion there is.

By receiver do you mean the tank?
And drain it by pulling the safety valve here:

Or simply attaching an air tool and draining the air that way?
Then remove the water drain valve that sits under the tank, i.e. this? But where it screws into the underside of the tank?

And by End Plug do you mean one of the brass end caps at either end of the tank?

 

[JonnyAlpha]

If it was me, I think I'd want to buy a compressor in better shape to begin with. After you fix all the faults it's still going to be a pretty beaten up unit, it really doesn't appear looked after, and there are loads about. Walk away would be my advice, too many faults on a cheap machine to warrant the time/money fixing them.

I'd prefer a better condition Compressor but I can't afford one however, before I shell out any cash in doing this one up i'll weigh up the pros and cons v buying a different one. I recon i'll get this for £30 which would be worth it even if I use it as an extra tank surely? (As long as the tank is in ok condition inside).

 

[Rig Pig]

Just drain the tank with an air tool or open port, unscrew the water drain from the bottom of the tank and see how much water and rust comes out, from what you said earlier it sounds as if the water drain is blocked? When you open the valve with 120 psi behind it you should get a good blast of air and any water that has dropped out. The big end plugs in the tank will allow you a peep inside to see how much corrosion has occurred. When you refit the valve and plug don't forget to use thread tape or a liquid equivalent to prevent leaks. If the tank is in a bad way or you need more receiver capacity you could always use another tank or old gas cylinder as long as it's purged of gas!

 

[Wallace]

Buy and use it as is, just through this thread you've repaired it to a usable state and learnt a lot. Spend £18 on a cheap 0.8mm gravity fed touch up gun and you can practice on the underside of the car with it and graduate to the outer panels with bigger and better set of kit.

 

[JonnyAlpha]

Just drain the tank with an air tool or open port, unscrew the water drain from the bottom of the tank and see how much water and rust comes out, from what you said earlier it sounds as if the water drain is blocked? When you open the valve with 120 psi behind it you should get a good blast of air and any water that has dropped out. The big end plugs in the tank will allow you a peep inside to see how much corrosion has occurred. When you refit the valve and plug don't forget to use thread tape or a liquid equivalent to prevent leaks. If the tank is in a bad way or you need more receiver capacity you could always use another tank or old gas cylinder as long as it's purged of gas!

I have removed the water drain from the bottom of the tank and as you suggested the tap was blocked with rust and crud. This is the piece that screws into the U Bend the screws into the bottom of the tank:

I cleaned out the U Bend and stripped the water trap with a wire brush and some emery paper and they now look as good as new. Only a tiny amount of water 'seeped' out when the tap was removed.

Next I stripped the head down to check the reeds, again as recommended, I have never stripped a compressor before so its all a learning curve.

Here is a pic with the cylinder head removed to show the reed plate, I had already lifted it off and put it back on to take a photo to ensure it went back on the right way around? Is this correct? The single round holes are on the intake side and the two cresents of four holes each are on the outlet side.

Lots of muck.

And here is a pic of the reed plate split, the wet is white spirit:

The reeds on this side are pretty mucky and I noticed the gasket had split between the two reeds on the RH side, I guess this is between the inlet and outlet of one of the two cylinders which would affect the performance slightly I guess?? Any idea where I can get a new gasket?

Here's the piston side of the reed plate:

And here are the tops of the pistons:

All the gunk on the tops of the pistons just wiped off.

I stripped down the reed plates and removed all the reeds and cleaned everything up with white spirit and wire wool. I also cleaned the inlet and outlet.

I then tried to remove one of the end plugs to inspect the inside of the tank, the two end plugs are about 34mm and I had nothing that big. One of the end plugs has another plug in it which is 22mm I think, this would not budge either and I did not want to force it. You can see in the pic below that it appears to have been repaired at some point possible braised maybe it had a 1/4 BSP screwed into it and since its been filled up.

I have soaked it with WD40 and will try again tomorrow.

If I want to run a hard line into this its going to have to come off but not until I have paid for it, if it wont come off I could run a line direct by removing the regulator?

I then removed the brass connector where the Air enters the tank from the pump to try and inspect the tank this way, the bottom of this plug was nice and clean but I could not see inside the tank with either of my torches :-( so as yet I have been unable to see the inside of the tank.

When I put this back together (if I get a new gasket) do you use standard gasket paste, the kind you used on a carburettors inlet port on a Motor Bike Cylinder Head, like Hylomar Universal Blue?

 

[ASL3312]

You seem to be doing a lot of work on someone else's compressor that you might not even buy yet!!

 

[JonnyAlpha]

You seem to be doing a lot of work on someone else's compressor that you might not even buy yet!!

That's the kind of guy I am :-)

But i'll be buying it anyway so nothing is lost.

 

[Rig Pig]

Buy a bit of gasket paper and cut a new one out, the replacement should go on dry with no nasty gloop. For the price your mate wants for it I would just go for it, it is a bit old and probably has a bit of work under its belt but it looks good for the price, just remember to drain the tank regularly.

 

[JonnyAlpha]

Buy a bit of gasket paper and cut a new one out, the replacement should go on dry with no nasty gloop. For the price your mate wants for it I would just go for it, it is a bit old and probably has a bit of work under its belt but it looks good for the price, just remember to drain the tank regularly.

The gasket that is fitted is pretty thick, but looks like its home made?

 

[mkelleci]

What should be the thickness of gasket sheet and gasket metarial?

 

[Rig Pig]

I would measure the old gasket and buy a some as near as possible to what was already there. Remove the old one as carefully as possible with a scraper and thin blade, clean it up and use it as a template to copy.

 

[eil]

Have you got four reeds there in total or am I missing something, the blown gasket would certainly be unhelpful in pumping up to pressure.

 

[Bill Edwards]

The thinner the gasket the better, until you reach a point where the piston hits the cylinder head. Fit a thin gasket and rotate the compressor by hand and check it turns freely without knocking or locking up.

 

[brightspark]

if the original gasket is say 3mm make the new one the same its that thickness for a reason

 

[JonnyAlpha]

Have you got four reeds there in total or am I missing something, the blown gasket would certainly be unhelpful in pumping up to pressure.

Yeh there are four reeds, the other two are attached to the other plate that sits on top of the one in the picture above, the reeds then operate in an opposite direction to the ones that you can see. two reeds for input and two for output. So the damaged gasket means there is leakage between input and output so when the Air is being sucked in some is going into the output without being pressurised but more importantly when Air is being pumped on the upstroke into the tank from one cylinder some is being forced back into the output, or so I have gleaned in my limited knowledge of Compressors. This would account for it taking 7 mins to reach 150 PSI, I am guessing with a clean up and a new / replacement gasket it will improve somewhat?

 

[JonnyAlpha]

if the original gasket is say 3mm make the new one the same its that thickness for a reason

Yeh, not happy to go any thinner as its working and would not want to risk breaking anything. The clearance also appears to enable the reed movement?

 

[JonnyAlpha]

Buy a bit of gasket paper and cut a new one out, the replacement should go on dry with no nasty gloop. For the price your mate wants for it I would just go for it, it is a bit old and probably has a bit of work under its belt but it looks good for the price, just remember to drain the tank regularly.

Why no gasket jointing paste? Or is that only required to prevent fuel / oil leakage in engines?

 

[Wallace]

With good flat surfaces and decent gasket material you should not need jointing compound.

 

[eil]

As Wallace says you shouldn't need gasket gloop with new gaskets but I would put a thin smear of contact adhesive or the spray on stuff you can get, between the gasket and face where its blown and tighten the head down then leave it to set for a while before running it up to pressure a belt and braces approach, the trouble with compound is people put way to much of the damn stuff and as well as making a mess it then gets to where it shouldn't be.

 

[JonnyAlpha]

The biggest source for Gasket Paper seems to be E Bay however there is so many to choose from. As the head gets hot will any type do or do I need anything special? I have found a couple of threads suggesting Klinger Gasket Materiel?