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AC Pumps - T Type - U type
#1
As can be seen on another thread the RP here conked out through lack of fuel yesterday.

It has a AC T type pump, the bottom half is actually fairly new, as supplied as a complete pump assembly by Jamie to father some years ago. Father clearly swapped the top for an old T type top. I remember something about sticking valves back then, but don't know the details. 

Anyway, It sounded like it was doing the business, but wasn't sucking fuel from the tank.

I've stripped it down, the diaphragm is all good, and the bottom end works as it should. The valves on the T type top are slabs of fibre with springs, and while these appear free etc, testing things out by blowing and sucking through various orifices suggests at least one isnt working correctly. Ive had them apart, saw no obvious problems, save fairly rough surface to the fibre and reassembled. Still the same.

   

Please let me know if the image do not work.

I do have countless other similar tops. but its obvious doing a google search that it seems to not be possible to buy the fibre slabs in a repair kit. 

However, I did find a brand spanking new U type pump. Different bottom end and levers, fitting this to the existing bottom seems to have got me a usable pump, which clearly sucks. The outlet is a little higher in relation to the pump body, but a quick anneal of the pipe and some bending will easily cure that.

As was

   

As is now on the Austin compatible bottom end

   

Am I missing something, but is there any reason a U type pump cannot be used?

It seems the U type has larger capacity. However my understanding was these pumps idle when the circuit between the carb needle valve and the top of the diaphragm is full. So it shouldn't make any difference. It might be better when the car is cold, the old pump struggled keeping up with che strangler engaged (perhaps a sign all was not well with it in hindsight)
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#2
Can the fibres be flattened on fine sndpaper? Are the seats bubbled?
The lever must contact the cam in centre of pad. Installation distance from cam affects pressure, as does internal spring.
Some carbs intended to work with crankcase vac have strong springs.  For the tinkerers, pressure can be assessed from a column of petrol! And gauges were commonly available. The hand lever pressure is not working pressure.
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#3
Hi,
The fibres are thin tuffnol which is a fabric and phenolic resin pressing.
If you sand it you might find that you expose more fibres which will not improve it.
You might find that fitting them the other way up might help.
Sanding Tufnol Dry is considered a health hazard nowadays.
800 or 1000 grit wet/dry paper used wet is fine though if you want to have an experiment. you can not make them much worse.
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#4
It seems the problem with the top that was on the car was the seat that was on the brass plate, not the one pressed in the body. The non return didnt seal. 

Having looked again in the shed I found a brand new and unused t type top. I thought I had struck gold. Unfortunatley the threads for the pipe fittings were different. 

So I used the valves, the disks etc out of that one. I cleaned the bits up (the brass was a little green) simply rubbing them on a piece of printing paper with some spittle, including the disks. 

So I now have a complete t type pump that sucks.  Its a bit feebler than the u type, but blowing and sucking through the relevant fittings confirms everything is working as it should now. 

Ill put it on tomorrow when I return from messing with the steam roller. Just need to find some card to make a joint.
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#5
'Morning, Hedd

Because you asked:   I never can see the images you post, I just get a string of letters and numbers inside brackets that identify the images.
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#6
Hedd, It is plain to see that you are also a steam man with your reference to joints rather than gaskets. Hope you are soon back on n the road.

John Mason
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
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#7
A friend of mine runs a '36 Ruby which had a AC "U" type pump fitted. He had a persistent dribble from the carburettor, despite new needle valves and all the rest. He replaced the "U" type with a "T" type and the dribble disappeared, so we assumed that the "U" type has a higher idling pressure (due to the spring??).

On the other hand, I've used "U" types in the past without issue...... Undecided
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#8
The spring in the 'T' type pump is weaker than the one in a 'U' type pump. I seem to recall that there was a thread on this some while ago.

I have a replacement 'U'type on my RP, as I had similar problems to those experienced by Hedd with the original 'T'type and ended up with the carb flooding. I think it was Ruaridh who put me onto swapping the springs over. Anyway, i hvaen't had any pump issues since.
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#9
I managed to find a brand spanking T type top. But the outlet female threads were smaller than the existing one, so I put the guts in the old top and reassembled. All is now well. 

I did find a source of the tufnol disks in America, but I think I have enough used ones to manage

   

Having a box load of bits, I thought building at least another working pump as a spare would be good. If nothing else for the tractor. I pretty much have everything I need save the seal that goes around the diaphragm rod to prevent crankcase oil getting in the pump. Anyone know where I can get one without buying an inappropriate 16quid kit?. 

   
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#10
These guys appear to have a selection, Hedd (without having to buy a full kit). You might have to scroll down the page a bit...

https://www.flexolite.co.uk/categories/f...fuel-pumps
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