The Craftmans Shop > New from Old
Steam Cleaner. Re-Birth of a Karcher MPDS
awemawson:
This afternoon, having first performed a bubble / leak detector test on the mornings air plumbing (all OK :thumbup:) I started on the valve grinding / lapping / recutting gizmo.
First I tested that cutting silicon carbide paper with the washer maker was practical - it is ! My 20 mm washer cutter is producing 21 mm washers so I had to go down a size.
Then I turned a 20 mm bar end down to 19 mm to clear the threads on the valve block, with a 6 mm spigot to locate the washer of wet and dry paper. I drilled and tapped the spigot M4, and made a 14 mm o/d 6mm i/d collar that slid onto the spigot to pinch the silicon carbide paper, and also form the guide bush in the through bore for the valves. This bush is retained by a cap socket screw and washer.
First tentative tests show that it seems to work quite well but I've run out of time and now need to do other things. The results in the picture are literally 5 turns of the tool lightly pressing it into place by hand.
tom osselton:
Not bad!
awemawson:
This morning I had a lapping session - firstly on the four valve seats that are fixed in the pump casting. They have come out OK'ish but there is still pitting apparent. I may have a further go at them tomorrow if I wake up full of enthusiasm !
Then I moved on to the disk valve face seals that press onto the valve seats by way of a weak spring. The first water inlet valve did have a distinctive shaped bit worn out of it which took quite a bit of work to bring up to a fair surface, but the other three weren't too bad - minor pitting.
There is a ball valve built into the casting of the pump, that apparently returns the output of one cylinder to the input side to halve the pumped volume when producing dry steam - I assume that the boiler cannot cope vaporising the full 1450 litres per hour that the pump produces and this seemingly reduces the flow to 740 litres per hour. Burner output is 420,000 kJ so some mathematically gifted person can no doubt confirm that!
I could find absolutely no way of removing the ball element, which has one quadrant as a plain sphere, two quadrants with a through drilling at 90 degrees the 4th quadrant being apparently not involved. This of course could be another path by which high pressure water is playing havoc with the input, so I wanted to examine the valve seat - sadly not possible.
I've decided to remove and blank off the twiddly bits that allow sucking in of chemical agents, and dosing with softening chemicals for the time being, I can easily add them back if and when I find I've solved the problem that I'm chasing and I don't want the complications that they add to the party.
Going through all my documentation for the hundredth time I've come across a drawing that implies that the pump may actually be a 'displacement pump'. This means no super tight cylinder fits, just tight packing to keep the water in. This technique is sometimes used with single acting hydraulic cylinders where the rod acts as the piston and the oil just displaces it.
I am fairly sure that the hydraulic accumulator that cushions pump pulses needs re-charging but I have no idea how to test it. The system operates (in theory) at 60 bar - does this mean that the compressed nitrogen in the accumulator should be at 60 bar ? If anyone is skilled in this direction please shout out.
awemawson:
I did in fact sneak out again last night and have another go at the valve seats - they are not perfect but will have to do - I'll see if they give issues when re-commissioning.
It occurred to me that it would be sensible to test the safety blow off valve before putting everything back together, so I rigged up my 'PRC1' test pump that goes up to 60 bar. Oops - the valve doesn't open at any pressure that I can give it - actually a bit more than 60 Bar according to the gauge :bugeye:
So I dismantled it for examination. It's a fairly conventional spring loaded face seal valve that probably would work very nicely were it not totally encrusted in lime scale. Now the book says that the safety or Pressure Relief valve should blow a bit when the pump starts - obviously it hasn't been doing this - is THIS our smoking gun ?
So a good soaking in citric acid and a clean up later it was restored to better health. I've set it to a conservative 40 Bar as it can easily be adjusted when things are back together and running.
I will also test the pressure switch that disconnects the electric clutch driving the pump before powering up. As I mentioned in an earlier posting I've never been happy that it's trigger point is correctly set, and with the PRC1 (which I'd forgotten that I had !!!) I can test it, but a job for another day.
hermetic:
after all this tension build up, only a video of you in a Santa outfit cleaning the JCB with the steam cleaner is going to assuage the yearning! I look forward to it!
Phil
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