mk1-forum.net

I am rebuilding several MkI Lockheed brake boosters.
Question: Was the non-return valve fitted to the booster? Or to the manifold end of the vacuum hose?
There is a non-return valve which screws into the booster body and joins the vacuum line from the manifold - p/n 17H2646. The original part has been unavailable for some time and has been substituted by an in-line valve requiring the vacuum hose to be cut.
Mini Spares now has the "original" non-return valve, made by/for AP.
BUT my supplier says that this valve must be fitted to the manifold end to allow vacuum to 'flow' from the booster to the manifold. It cannot be connected to the booster body because it won't flow in that direction.
Is AP wrong?

should be screwed in to the booster (servo) body

the modern ones screw into the manifold

i.e they suck through the thread

I've got two cars from the same era each with a different location for the non-return valve - one on manifold, the other on the booster

Mine's work with the non return valve on the manifold. The socket on the booster is just a socket. I really wonder how some one gets vacuum on the booster with a non return valve on the booster?

It depends on which way round you put the valve you are just mooving it further down/upstream, as long as the valve is orientated the correct way it will make no difference where it is in the line.

Thank you all for replies.
All very interesting - that there were valves that went on the booster (blew) and those that went on the manifold (sucked).

Aussie Bill B wrote:Thank you all for replies.
All very interesting - that there were valves that went on the booster (blew) and those that went on the manifold (sucked).

Caaarrrm on... its a one way valve. Air passes one way and not the other...It doesn't suck or blow.

As has been pointed out, functionally it doesn't matter where it goes in the line - as long as its the right way 'round.

Otherwise its trainspotters argument.

For arguments sake though... my BMC workshop manual (circa 1967) contains the statement "Unscrew the non-return valve from the side of the slave cylinder." as the final step in disassembling the booster. Unfortunately I have no idea whether this is a Lockheed or Girling unit - other than its the type fitted to a Mk I S.

Cheers, Ian

1071 S wrote:Caaarrrm on... its a one way valve. Air passes one way and not the other...It doesn't suck or blow.
As has been pointed out, functionally it doesn't matter where it goes in the line - as long as its the right way 'round.

I totally agree with this!

As far as I am aware, the main purpose of the valve is to prevent destruction of
the servo unit in the event of a "back-fire"...

It allows the engine's vacuum to suck on the servo unit to produce extra braking,
but will not allow any manifold explosion back up the pipe which would damage
the diaphragm.

There is nothing technical about this at all...
(But if you are an electronics nerd, it's a "diode").

Ian

The main purpose of the valve is to hold the vacum in the booster chamber, otherwise you wont get constant vacum .

cpr1 wrote:The main purpose of the valve is to hold the vacum in the booster chamber,
otherwise you wont get constant vacum .

I'd go with this answer, with my own attempt being relegated
to a secondary benefit...

Ian

Does this answer your question? Fresh out of the box

Toby wrote:Does this answer your question? Fresh out of the box

Thanks Toby.
The photo shows the one-way valve is on the body of the booster. But does it allow air to flow out of the booster or into the booster? It must let air flow from the threaded end of the valve to the hose barb end of the valve to create a vacuum in the booster for it to work.
The new valves from Mini Spares fit onto the manifold and so only allow air to move from the hose end of the valve to the threaded end of the valve, into the manifold vacuum.

Caaarrrm on 1071S... it does have to be the "right way round" and that's the point of my original question. You cannot reverse the valve.It's nothing to do with trainspotting.

1071 S wrote:Caaarrrm on... its a one way valve. Air passes one way and not the other...It doesn't suck or blow.

As has been pointed out, functionally it doesn't matter where it goes in the line - as long as its the right way 'round.

Correct. But the point is not all the valves let air move in the same direction. Hence the original question and hence it makes a difference where you fit it. If the valve lets air go from the threaded end to the hose end, it goes on the booster. If it lets air go from the hose end to the threaded end, it goes on the manifold.

Thank you abri. That is exactly my point.
As several answers have said, there are 2 kinds of valve getting around.

The valve shown on Toby's picture lets the engine suck the air from the servo, ie, air passes from the servo end to the hose end.

The following 2 types work on the opposite manner. I don't know about modern stuff.

The engine must be able to suck the air from the servo ("vaccum booster"), so you need to fit the valve that allows it to happen.

Thanks Ricardo for the photos.
It makes some sense, although I've never seen those valves fitted to the manifold.
Bill