mac valve for my step well ram leaks out the exhaust port.

HI can anyone chime in. I have replaced my mac valve that controls my step well slide twice. leaks out the exhaust port when off. ? thanks. 99 marathon.

Mine did same thing,even new one. Valve needs a bit over 20 psi to move to close

Its the internal oring on the bottom of the ram on the cylinder itself thats bad and the leaking air is coming out the exhaust on the Mac valve.

thanks joe. i can buy that one. but if the mac is not powered seems it should not pass air thru. am i thinking wrong. or is the air stored in the ram thats leaking ? its leaking when no power to the valve .and step slide not in use. i have a new norgren reg set at 19 lbs and it leaking at the exhaust.

This is what Joe is talking about. If air supply to retract the step slide is passing by the piston seal, it will show itself by escaping out the exhaust port. Same thing can be said for the other direction. Follow the Red arrows.
http://forum.prevostownersgroup.com/...id=16971&stc=1

Here is a very simple illustration of how a valve and cylinder work.
https://www.youtube.com/watch?v=iIMgJ-wa0Y8

That ram is pressurized both ways open and closed so if that internal oring on the bottom is leaking it comes out the mac exhaust port.

Marathon does a very complete job of building a very solid structure with the step slide. That cylinder is boxed in but good. Get some directions from Marathon as to the cylinder removal before u start, I would.

Did the first replacement of the Mac valve work? If so, you might take the old Mac apart and make sure it had nothing obstructing it. I have had success in doing a VERY CAREFUL disassemble making sure there is no obstruction in all of the ports, and bench testing before reinstalling. It is worth a try. also, make sure there is no moisture getting to the Mac.

THANKS i get it. i was thinking no air passed thru till powered. but is pressured all the time. i think an air off / on switch on the input is the best way to go. one more thing i have heard air woose when i close the generator bay door. my generator air bags have schrader valves on each bag. is what im hearing another mac valve for the generator bags ? but not plumed in. ? thanks for the help everybody.

Mike, great picture to illustrate how most pneumatic rams and valve controls work.

Your gen bags r isolated from everything else if u see Schrader valves right on them. Good. Simple.

thank you.