The Stovebolt Site Forums The Parking Lot Big Bolts A hydrovac question

My 42 1.5 ton does not have a check valve in the vac line. How bad is this and what should I be checking for, for proper ops of the system? Where can I get a check valve ?
Thanks for any help

I know that there have been some threads on hydrovacs here so if someone could post the links I would like to read up on them.

You don't need it for proper operating of the hydrovac.

All it does is to fall down into place when the engine dies, effectively leaving vaccuum pressure in the system so you will get one or two presses of the brakes with the hydrovac helping.

You can get one in most large trucks from the 40's through probably the late 60's. A lot of different makes and models used hydrovacs.

Jeff

I've been told that the check valve keeps any raw fuel or contaminants in the intake manifold away from the rubber diaphram in the H-Vac unit that would shorten it's life. You should probably look into getting one for your truck sooner than later.

-Mike-

Hy Rix42, welcome, the check valve is there to stop the hydravacs vacuum from disappearing when you have a low vacuum condition occuring in the intake manifold, such as when you're climbing a hill. Without the check valve the vacuum available to the Hydrovac would be constantly fluctuating, hope that helps.

3B, interesting point, I wouldn't have thought of that. I would have figured the vaccuum would still be enough to operate the hydrovac under extreme throttle, but maybe not.

Jeff

Thanks for the help. I will see I can find for a check valve. I want to see what difference it makes if any and I also read that the flow of oil or gas fumes can damage the diaphram in the hydrovac. So that alone would make it good to have.

Well I checked around and came up with nothing useable sooo... Does anyone have a part number that would work for a check valve?

The vacuum lines are also routed with an upside down U bend mounted on the fire wall that has the top of the bend higher than the carburater. This keeps the gas fumes (heavier than air) from migrating into the storage tank and condensing back to liquid gas. Look for the parts from a donor truck.

Mike B

If you are not going for a 100 pt. restoration most any modern truck uses a check valve for the manifold vacuum line to the power brakes and one of these could be adapted if you can't turn up an original.

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The U bend in the line only makes sense but it never registered with me what it's purpose was. I always learn something on this site!

ok I will continue to hunt. Thanks for the help My vacuum line does loop up over the engine and down to the manifold to at least that should help with the fume problem.

The check valve also helps save the vacuum system when the engine back-fires through the intake manifold/carburator. If the storage tank is full of fumes it could blow...

Mike B

I don't want that to happen. I'm still looking for the moment.