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Bleed valve

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Paul Lousick05/07/2019 08:35:37
1149 forum posts
492 photos

I have completed the manufacture of a lubricator for my traction engine and would like to add an in line bleed valve to the oil feed pipe. Very handy for removing air from and for checking if the pump is working.

Does anyone have a drawing to suit a 1/8" OD tube ?

Paul.lubricator.jpg

Nigel Graham 205/07/2019 09:50:17
356 forum posts

Afraid I can't help with drawings, but on the first point I think you are worrying unnecessarily. The oil will soon purge the pipe by merely pushing the air into the steam-chest.

Assuming normal practice, in which the oil-pipe is connected to the steam-circuit simply by a union nipple:

I think you will find a test-point as you suggest will not really test anything because the pipe is open-ended either effectively to atmosphere when the engine is cold, or to steam in running conditions.

In normal service the lubricator soon reveals something is amiss by the oil-level not dropping; and I have never seen nor heard of anyone fitting a bleed-valve in the oil-line, in miniature or full-size.

'

Under running conditions a bleed-valve between pump and valve-chest will simply emit a lot of steam. A pressure-gauge there would show a pressure - but of what? Oil or steam? Or some resultant pressure? It will not show oil is actually being delivered to the steam circuit, though a blockage downstream might create an oil pressure above boiler pressure.

Used cold, and turning the lubricator manually, the bleed-valve will emit some oil, but most of the oil will take the easier exit, into the steam-chest. A gauge will show if the pump can give adequate pressure only if the pipe's outlet is plugged, or the gauge is connected to the pump directly - i.e. no outlet for the oil.

'

So where does this leave us wanting to test the mechanical lubricator?

In service: A mechanical-lubricator is self-purging, and shows it is working by the oil-level falling. And by very oily soot in the chimney top if set to be a bit too generous - at least erring on the safe side.

Cold: The lubricator can be tested new, after a service or if suspect, for flow by an open outlet, and for pressure, by direct connection to a pressure gauge; and manual rotation.

The oil-line including any in-line check-valve can be tested (I have known them become blocked) only with the engine cold; by disconnecting the delivery end and again, operating the pump manually.

Paul Lousick05/07/2019 11:37:52
1149 forum posts
492 photos

Thanks Nigel,

We have bleed valves on the lubricator on some of our full size engines which I operate and find that it is convenient for checking pump operation without having to break the supply line. Plus its another feature to add to the model.

Paul.

JasonB05/07/2019 11:47:30
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15988 forum posts
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A bleed valve should not emit steam as there are usually a couple of check valves in the oil line, one as it exits the lubricator and another as it enters the valve chest..

If the pipe is full of air there is a risk that the pump will just compress that air against the check valve springs's pressure and you won't get flow even if the pump is working OK.

I would have thought a simple tee in the line with a cap/screw to bleed would work or make the check valve that fixes to the valve chest with a branch that can be used to bleed it.

Paul Lousick05/07/2019 14:00:39
1149 forum posts
492 photos

Jason,

The one on our Fowler TE is like a tee with built in needle valve. I could design my own, just asking if anyone has an existing design first.

Paul

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