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Repairing a Hodge Clemco 1440NC Blast Pot

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awemawson:
While stripping paint on some panels on my JCB 3CX ready for painting my Hodge Clemco 1440NC blast pot jammed up - the rubber conical valve that raises to seal the pot when blasting, and lowers when the dead mans handle is released (to admit more sand from the hopper) wasn't raising thus not building up pressure.

At first I thought that the rubber cone itself was jammed but no - having emptied the pot and removed the mud hole to access the valve it was moving freely - perhaps slightly eroded on the rubber but it looked as though it should function were it pushed up into the matching rubber ring in the lid of the pot.

Now pilot air passes down a thin pipe to the operators dead mans handle, and back up to an 'RMS100D' control valve that operates the rubber cone and equalises pressure in the pot. It has jammed before and I had to clean it out but I can find no record of the pictures that I took then - I'm sure that I posted them on the forum but . . no gone  :scratch:

So today's job was to remove the valve, dismantle it and assess the damage - they are about £240 to replace but a seal and gasket kit is available for about £30. Hopefully it's rebuild able.

There is confirmatory evidence that I'm not dreaming and indeed have been here before by the alignment marks I've put on the body of the valve.

awemawson:
Now the first thing I noticed was that the 3/4" 'street elbow' that connects the valve to the silencer had worn right through at the bend ! Now this is nothing to do with the fault but shows how abrasive sand is.

Pulling it all apart the upper valve, piston and associated seals look to be fine, but the lower valve was very stiff (probably the fault) and the aluminium piston is scored but the bore of the cylinder seems OK. The seals are O rings and once the scoring is cleaned up I don't think its sealing properties will be compromised too much.

Rooting about in my bag of old iron plumbing fitting I actually found a rather tatty street elbow - a bit of blasting in the cabinet blaster and a light spraying with galvafroid and it looks almost presentable.

So, quite successful so far - I'll order up a rebuild kt that has the necessary O rings, diaphragms and piston seals and I'll probably replace the rubber cone valve while I'm at it. Vendor on holiday until middle of next week so watch this space.

awemawson:
The new Popup Valve and it's rubber seating ring arrived yesterday so one of today's jobs is to fit it.

The mushroom shaped valve is rubber faced and sits on a vertically mounted 1-1/4" BSP pipe - air entering the pot blows it upwards making a seal with the big rubber O ring in the top of the pot. This allows the pot to pressurise and then pot pressure holds it in the sealed position.

This means that to replace it you have to open the 'mud door' and unscrew the standpipe allowing the replacement of the two sealing components - mushroom and ring. Not particularly complicated just a bit awkward to get at and see what you are doing. To get at the ring I took the upper shield off - just a plate held on by three screws that prevents a weight of sand in the hopper affecting the pop up valve.

Did I NEED to replace the pop up valve and ring - probably not. I can see some erosion in places on the mushroom but not a lot - I'll certainly keep the old one as an emergency spare.

Still waiting for the bits for the RMS100 remote control valve rebuild.

awemawson:
The rebuild kit for the RMS100D remote valve came in this mornings post so I started rebuilding the valve.

Removing the O rings from the two piston assemblies I lightly cleaned them of scuff marks with fine wet and dry paper, gave them a thorough clean up and refitted the O rings with the slightest whisper of petroleum jelly as recommended by the makers.

Then it came to replacing the actual piston seals. Now these have not been removed by me, either on this repair or on the one previously but I noticed a VERY odd thing. They are perfectly normal 'lip seals' where the lips are usually installed facing the source of pressure. This allows the pressure to push the lips tightly against the cylinder bore making a good seal. Now the upper 'exhaust piston' seal was indeed this way round the but other one was the other way round. Now the operating pressure source for these pistons is introduced between the two pistons so I cannot imagine that it is correct that one is reversed. In the absence of being able to find any detailed drawing I have assembled them 'lips to pressure' - if it proves wrong I'll have to pull it apart again !

So carefully cleaning the cylinder bores I re-inserted the pistons and built the unit up to the stage that I could introduce operating pressure to the port that would normally come from the dead mans handle to prove the pistons moved satisfactorily. Fortunately they did - I had to return them to the un-operated position by hand as this would normally be done by the pressure in the pot (which is not yet attached!)

So far so good - putting the rest back together was pretty simple except that there was some fretting between the exhaust cap and it's mounting spigot that I had to clean up before it would seat nicely.

Putting it back on the blast pot was also fairly simple - the silencer is at a bit of a jaunty angle as I've obviously not got the valves top cap quite where it was originally - I may loosen it all off and get it back vertical later but just now I'm committed to being 'mine host' as the most recent cottage guests have just pulled into the farmyard so I must run  :bugeye:

awemawson:
So having duly installed the guests in their cottage - (and most importantly shown them the way to the pub !) it was the matter of a few moments to slacken off the fittings and rotate the joints so that the silencer is more vertical.

it cannot be exactly vertical as it clashes with the pressure reducing valve one one side and the body of the pot on the other, but I very much doubt that the exhausted air will mind much !

I can't test the pot in earnest as a further set of cottage guests are expected - it'll probably be a day or two before I get the chance as it means running up the rather noisy road compressor and dragging out all the paraphernalia of hoses, bags of sand etc.

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