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Old 11-30-2020, 07:36 AM   #1
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Year: 2003
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Pneumatic door issue

I'll admit that i know little when it comes to the air system of my bus but i understand the core principals. The service door on our bus uses an electric rocker switch in a neutral position, up activates one side of the cylinder of our door (open) and it returns to neutral, down activates the other side of the cylinder (closed) and returns to neutral.

A short time ago i noticed the sound of air leaking when i shut the door and traced the sound to what I can best describe as a plastic screw plug that can be hand tightened so i snugged it i and the sound stopped. Until last night.

I tried tightening it a bit more with a set of needle nose to grip better, no luck. Tired thread tape, no luck. I even tried pulling the plug from the open side and still no luck. I've not got a lot of clearance on the back side to see what I'm looking at but I'm afraid I've got a crack. Figured I'd seek advice from those more experienced to see if anyone else ran into a similar problem.

Also it looks like the district cut some writing and did a bit of splicing to the mechanism, if anyone is able to explain that i would be very grateful.Attachment 5152820201129_174828.jpg20201120_125430.jpg
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Old 11-30-2020, 07:37 AM   #2
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I forgot to indicate which one is the issue20201130_073702.jpg
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Old 11-30-2020, 12:19 PM   #3
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Year: 1935
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Engine: 317 ci/tid / Isuzu
There is a spool valve in the center portion of the valve which is pushed one way for open air and the other way for close air by the solenoid located on either end. The part you have circled is an exhaust vent and will give a quick psst sound upon opening and closing the door. If it is continuing to vent it means that the spool valve isn't in the correct position and is bypassing air.

These valves are very fussy about contamination so it is important that the applied air be clean and dry. A little water in the line and a hydrostatic lock can occur or in cold weather ice can form in the valve. The solenoid valves sometimes jamb and sometimes grow weak either of which can result in the problem you have. The pair of hand adjust valves control the speed of door action and their knurled collar tighten the packing around the stem--like in a sink faucet.

When my bus door did this (and I wouldn't recommend except as a last resort) I took the entire unit apart and cleaned it out. As I look at your setup I'd start by making sure the air tank was well drained and then refilled. Next I'd disconnect the inlet line to the door valve and let the tank thoroughly blow out the line. Next Id' re hook up the line and disconnect the lines where they enter/leave the slave cylinder and cycle the open/close switch a number of times which hopefully will rid the system of any contaminants.

If none of this helps check on ebay for a replacement and then tear the valve apart. Good luck.
Jack
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Old 11-30-2020, 12:24 PM   #4
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Could putting a bit of pressure against the door in one way or the other help as well? Or is line blow of about the only fix other than taking the thing apart?
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Old 11-30-2020, 12:27 PM   #5
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That may clear the spool valve temporarily -- give it a try.
Jack
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Old 12-07-2020, 01:39 AM   #6
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Year: 2006
Coachwork: Bluebird Chevrolet short bus
Chassis: Chevrolet 3500
Engine: 6.0 Gas hog
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it may not be the spool valve, I would take the line off of the cylinder one side at a time and see if the air keeps bleeding off at the valve or if it starts to bleed off at the cylinder where you disconnected it. if it starts to bleed at the cylinder connection, Then the cylinder is faulty and the packing glands need to be replaced if you can find them. If the air continues to bleed from the valve, then the valve needs attention. It can be purchased in pieces so you do not need to purchase the whole thing. Just the center body usually takes care of the problem. If you discover the faulty part, a bit of air line antifreeze blown thru the air valve or cylinder liquidates the oil and dirt buildup and sometimes frees the seals. Be warned tho, too much air line antifreeze will dry out seals also. Use as a last resort before making a purchase
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