Parking Brake Valve trouble potential

[SierraYankee]

Dear Skymaster pilots and mechanics;
what are the possible troubles a malfunctioning parking brake valve (the entire unit) could cause ? This is for a P337H, SN P33700305
Could a leaking valve cause brake pressure loss in both L & R sides ?
Could a 'broken' valve cause air to entrain into hydraulic lines, or oil leaks.

Any conceptual thoughts would be of help.

Thanks in advance

[mshac]

My understanding is the parking brake valve closes the brake line while pressure is held on the brakes, allowing the brakes to stay "set", with the pressure remaining in the line.

A failed parking brake valve would potentially keep you from setting the parking brake, but unless its also leaking fluid, I don't see how it could affect your brakes.

Attached are a few relevant pages from the P337H service manual:

[SierraYankee]

Thanks for the informative reply and relevant pages.

Can the parking brake valve (if physically damaged) cause air to be entrained in the brake lines ?
My brakes keep losing pressure and oil, and every 4th-5th landing the master cylinders need to be replenished. No oil on the floor or belly (unless it is squirting out on the runway during landings).

[mshac]

It certainly could. Have you removed the cover panel and inspected the valve for leaks? That brake fluid is going somewhere. You may find your sound deadening fiberglass near the valve is saturated with 5606.

[SierraYankee]

No oil leaks evident from the brake valve

[mshac]

5606 is red out of the can, but if exposed to air and light it will turn clear. I would take another hard look a the entire brake system. Any fluid could be your leaking 5606, and it may not be obviously red.

[SierraYankee]

Greetings Folks;
anyone have a diagram or sketch of the C337 parking brake valve.?
Need to see if a worn valve could leak 5606 fluid simultaneously from both Left and Right hydraulic lines.
THANKS in advance

[Dan schultz]

Yes it can if the seals are bad. Mine had a bad bore and I sleeved it. Make sure to undo the fittings to get the small pins out so you can pull the actuator rod out. The actuator rod has the seals on it.

[SierraYankee]

Thanks for the info Dan.

[Kim Geyer]

I’ve had to reseal several valves. As a matter of fact I had a spare valve I would rotate around