Steam Cleaner. Re-Birth of a Karcher MPDS

[awemawson]

When I moved to the farm here eight years ago I needed a stand alone pressure washer - ie independent of electricity or even piped water as at that time I hadn't put services everywhere and yet I was churning up loads of mud with my JCB 3CX. It was of course putting in those needed services 

Casting around I came across a military version of a Karcher Steam Cleaner. Powered by a diesel engine, and burning diesel to heat its water, it could suck up its water supply from a pond or stream and seemed ideal, if a little large.

When it arrived it turned out that it was an 'MPDS' or Multi-Purpose-Decontamination-System. Intended for field deployment on the German Plains as the Russian hoards swept over using battlefield nuclear weapons, this would hopefully clean up tanks and vehicles as well as personnel.

I managed to find the military instructors guides on the web which I attach to this post

Superb beast driven by a Farymann 6.5 hp diesel engine, one of which I already had on a larger vibrating 'wacker plate' so I knew the engine.

[awemawson]

Over the years it's given me good service, with the pressure washer bit never letting me down. However the steam side became more and more un-reliable - not firing up on demand. At various times I'd done bits of investigation but never managed to bottom the fault(s) so resolved to have a 'good go' at it.

Problem was that the control box is tightly packed, has numerous relays, and although I have a circuit diagram, relays weren't numbered so it all got a bit confusing. I'd had my suspicions that the 'flame failure' circuit was at the heart of the problem, but it's control box was buried deeply in the main control box, and anyway couldn't easily be tested unless in-situ and connected to it's various peripherals.

I decided to bite the bullet, pull it out, and configure a test rig for it so that I could test it on the bench.

[awemawson]

Pulling the Flame Failure unit out was a bit of a hassle involving taking much of the surrounding controls and indicators off first, so  a very methodical approach was needed if wires weren't to be misplaced.

Eventually it came out

[awemawson]

The first thing I did was a careful visual examination which revealed no obvious issues, then I went through all the components to ensure spares were still available. They were, albeit that that i/c (which is a window discriminator) was being offered on eBay at £75 !!!!

So what does it need to work? Well it wakes up by being supplied with 12v DC. Then it monitors a Cadmium Sulphide photo-cell that is looking into the combustion chamber. It needs to see no light at this stage which is high resistance of over 1 Megohm. If this is the case it turns on the relays controlling the fuel and ignition. Then in the next ten seconds it needs to 'see' light via the CDS cell, represented by a low resistance of about 400 ohms. If this happens then the ignition is cut off, the fuel left on, and it sits in that state until either the flame goes out or the 12v is taken away.

It proved impossible to easily remove the original CDS cell to use it in the test rig as it was hard wired, so I measured it's characteristics and used resistors to emulate it's two states with a toggle switch to select flame or no flame. 12v torch bulbs were wired as the  three outputs (Ignition, Fuel and Fault)

[awemawson]

The mounting of the CDS cell was rather Heath Robinson - it must have been replaced at some time and was a different diameter to the housing, also the housing had to be spaced off the boiler by a pile of washers to allow for various flangy bits. So I re-engineered it all, turning a ptfe collar for the CDS cell and specific spacers to replace the washer pile - sorry no pictures.

Well the test rig worked splendidly. I could not only prove that it went through it's various sequences, but also that it was able to take a reasonable degree of 'tap testing' and voltage variations.

On the face of it slightly disappointing that it wasn't the fault, but in fact actually re-assuring that now I knew positively that it was working and could be eliminated from the diagnosis.

[awemawson]

So now I turned my attention to the ignition side of things. There are two 'spark plug like' electrodes protruding into the flame chamber close to the fuel jet. These are fed by screened EHT leads (military remember so EVERYTHING is screened) emanating from an EHT transformer whose primary is 240v mains. No mains in this device so another unit described on the circuit diagram as a 'transformer' but infact a transformer driven by a transistorised inverter, takes in 12v DC and outputs 240v. Initially I was convinced that the screened leads were 'leaky' as measuring to frame I was getting only about 50 kOhms - then it dawned on me that the EHT transformer secondary was 'centre tap earthed' so I was measuring half the secondary winding resistance 

So a quick test: I rigged up a lab power supply to the inverter and sure enough nice crisp discharge crackling could be heard (10 kV at 20 mA). I re-terminated the EHT ends as they were rather frayed and put it all back together.

[awemawson]

For the CDS control box to fire up the boiler a few other conditions need to be correct. One is a 'flow switch' needs activating by pulling the trigger on the lance.

The flow switch is mounted in a dual purpose housing (it has the main pressure switch in it as well) but this flow switch has a magnetic shuttle that is pressed 'left' by a weak bronze spring, and 'right' by the water impinging on it. The magnet operates a reed switch in an external brass tube.

I had tried operating it by pressing it 'right' - there is a filter plug that can be removed and an allen key would just reach round the corner and press it - sure enough operated according to my meter. However measuring is real operating conditions it didn't work - all very odd 

Next I made a bit of an error 

I decided to unscrew the plug that gives access to the bronze spring and magnetic shuttle. It went ok until, having difficulty getting the shuttle out, I turned the water on. Of course - obvious realy- the shuttle shot out like a bullet from a gun 

I  eventually found it after a bit of searching, but now I didn't know which way it was supposed to face.

[awemawson]

Now initially I had though that the large end should face the incoming water, but then I noticed the 'screwdriver slot' in that end - this could only be accessed from the right. Both ends of the shuttle had turned down sections that nicely matched the spring diameter so no help there 

I put it in 'screw driver slot right' - tested it with the allen key trick through the filter plug - which worked - and then tried it under operating conditions. No go, still not closing the reed switch.

Well - nothing to lose I pulled it apart again this time putting a rag over the opening to catch the shuttle  then re-assembled it 'screwdriver slot left'.

  Hey it now works 

Now the magnet is very weak and various descriptions of other Karcher pressure washers say to change the magnet annually. So I've ordered another one. BUT - it begs the question - was it in wrong to begin with. The only other explanation I can come up with is that I did ease a few slight burrs on the shuttle - was it perhaps jamming. Anyway at this stage she fires up on demand.

Just two more issues to resolve:

 Firstly there is a two way fuse box that seems to be described as a 'continental type' holding the style of car fuses that are pointed and sit between springy brass leafs with location holes. One way was weak in the springyness department and I'd temporarily wired it out. Someone had packed the other way with a screw to give it more oomph but it needs changing. (The holder on the left is an 'indicating' ie has a neon across it - 2A mains fuse for the inverter circuit)

Secondly there is a persistent diesel leak with diesel running out of the vortex chamber of the main blower fan - not healthy

[awemawson]

After much searching I managed to locate an exact replica of the two way fuse box - at one point I'd thought I'd have to use 'in line' fuse holders as space is very tight, but this turned up.

Joy when it arrived - EXACTLY the same size even down to hole mountings - joy was soon dashed when I took it off the vacuum packing and found it cracked 

[awemawson]

Never mind - the seller seems to have loads and is posting another one, having first unpacked it to check it hasn't suffered the same fate !

So on to the diesel leak:

Close examination revealed that the diesel was coming out of the rear of the injector pump so I rather expected major mechanical issues with the pump itself. It looks almost identical to a standard oil boiler injector pump, just not quite the same 

Then is occurred to me - in the book of words for this machine I have a parts list where all the parts have NATO stock numbers - Google the NSN ! This not only told me it was a SUNTEC pump, but one was for sale in the USA on eBay !

However it also allowed me to identify the model and get the makers literature. This showed me that there was an oil seal on the drive shaft, that is in a chamber that is filled by the oil retuning to the tank. Hence not huge pressure. It also allowed me to locate the very same exact seal on eBay in Germany - it's a bit of an odd size - 8mm shaft but 26mm outer diameter.

Seal duly ordered and arrived this morning

[awemawson]

So I whipped the pump off, revealed the seal, undid a circlip, used a rather crude method of removing the seal (how else??) popped the new seal in and she works a treat. No more dripping diesel.

It turned out that the entire inner lip of the lip seal had come detached from the body and indeed remained on the shaft when I took the rest off - never seen one so bad before !

[awemawson]

So just that fuse holder to sort, and probably a bit of wiring tidying up and she should be good for another 8 years 

[hermetic]

And better than it has been for a long time, good work Andrew!
Phil

[Pete.]

Noice work

[mattinker]

So, this is what you've been up to recently nice to see
 you've been having fun!

Regards, Matthew

[Kjelle]

It's alwas fun, and educating, to read about your projects... It's not often I can contribute to what you are doing, but now, for once... The fuse, ceramic body with pointy ends, are called "Bosch" type in the automotive world. Quite common in German cars up to the late 70's-early 80's. Renowned for oxidizing between the ends and the holder, causing problems... Nope, I don't miss'em!

Kjelle

[jcs0001]

Andrew

Interesting project and nicely documented.

John.

[awemawson]

Thanks chaps for the kind words.

That replacement two way fuseholder arrived this morning, so I've fitted it and sorted out one or two other little issues.

I noticed that there was no stopper for the filling orifice for the high pressure water pump - no idea whether it had always been missing or if it's a recent loss, but I made another out of a bit of stainless bar - also no idea what the original design was but I'm sure that this will fit the bill.

I replaced the engine air filter, as I happened to have one in stock, and ordered up an oil filter. When it arrives I'll drain and flush the oil through with a new fill using the old filter, then replace filter and oil again - it only holds 1 litre so no great volume. I'll also drain and refill the high pressure water pump oil at the same time.

I've also at some time to replace the fine brass gauze that stops muck entering the diesel pick up pipe. There is a standard Jerry Can built into a holder in the main frame, and it has two 10mm brass pipes dipping in, that were originally protected by a wrapping of gauze soldered on forming a filter. Over the years the ends of the pipes have bashed their way through the  gauze making it useless. I have a bit somewhere and when it turns up I'll effect a repair.

Meanwhile I gave it a good testing blasting away the moss that was growing on the ramp that leads up to my loading dock - it had got so bad that the forklift would sometimes slide down with locked wheels!

I burnt about 10 litres of diesel in 2 hours - I was 'steaming' rather than just using pressure really just to test the machine. Apparently it generates 390,000 BTU  or 114 kW of heat 

[Spurry]

Yet another superb job 
Pete

[sparky961]

Gotta say, I'm a bit jealous of your troubleshooting prowess.  I have a lot of the knowledge required to figure out problems like that but end up frustrated at the lack of information usually available.  I've also made mistaken educated guesses in the past as to how many volts to apply to what and where, resulting in the release of the "magic smoke".

Sounds like you have a very robust unit there, and under your care it will likely outlast you.  Nice to see that some things are still made to be fixed and to last.

[awemawson]

The secret Sparky is to spend a life time with not quite enough finances to do what you want without doing it yourself - they say that necessity is the mother of invention 

Now having this machine reliably working again is proving SO useful - I've just started working on my ancient Thwaites 2 ton swivel dumper. I've had it  nine years, and even when I got it the forward cylinder has been reluctant to fire up when cold. In all that time it's never come to the top of the list to be worked on, but now it's got so bad something has to be done.

It's a Petter PH2 engine with electric start. Years back I've proved diesel is getting to the forward injector, and even swapped the injectors to see if any difference, so I strongly suspect poor compression, either worn bore or burnt valves.

So back to the steam cleaner - I hate working on oily grubby engines (which is probably why I've put this off for so long    - you could barely see the fins on the front cylinder barrel it was so gunged up - but 3 minutes with the steam cleaner and it's quite nice    Mind you it takes paint off as well.

[awemawson]

The other day the new oil filter arrived for the Steam Cleaner, so I flushed it with new oil - twice actually as a lot a gunge came out, then drained it again and refilled with clean oil and the new filter. I also drained and re-filled the high pressure water pump as it takes the same oil, and re-greased it's sliding bits. So it's now had a full in depth service which is re-assuring for it's future longevity.

The steam hose is rather cumbersome to wrap up after use - it's 3/8" bore two wire DN10 hydraulic hose rated at 490 BAR and 150 deg C with an outer diameter of 3/4", so although it bends OK, it doesn't twist at all and fights you when trying to coil it. So I've decided to make a reel for it, and fit quick release fittings on the ends, which will also act as swivels.

Proper high pressure high temperature steam reels are available, but at enormous expense - over £200 for one whose reel diameter is large enough for the minimum bend radius of the hose  so I've bought these redundant fire hose reels off ebay and will modify them - one for the feed water (may not need modifying), one for the high pressure, and the other can be a 'shelf spare'

At £20 each I reckoned that they were worth a punt 

[nrml]

Yet another great thread ! The only problem with reading your threads is that I always end up thinking 'I'd like to have one of those..... Would be very handy.' I end up wasting a few hours on ebay before reality eventually kicks in and I realise I couldn't use whatever I was searching for to a fraction of it's potential either for lack of knowledge how to or lack of playtime .

The thread that got me sidetracked the most was your wire EDM restoration project. I actually ended up bidding on one before I came to my senses and realised I would spend a few years learning how to use it. Luckily I didn't win it.

Looking forward to your next project.

[Pete W.]

SNIP!!

.... so I've bought these redundant fire hose reels off ebay and will modify them - one for the feed water (may not need modifying), one for the high pressure, and the other can be a 'shelf spare'

At £20 each I reckoned that they were worth a punt 

So, Andrew, all you need now is a spare reel on which to store the redundant fire hose when it's replaced by the steam hose!!!!           

[awemawson]

Well I reckon that I now know what happened to the original stopper for the pump oil reservoir - it popped it's cork  I noticed the other day that my nice new stainless stopper had raised until it was resting on the O ring seal. If it had been lighter it would have gone the way of the previous one. Presumably there is back pressure when the pump is running, and the only vent is via the filler.

I ordered a commercial 3/8 BSP filler / breather unit and drilled and tapped my stopper to take it - hopefully now it will remain in place.