Pressure Protection Valve

[Curt Sprenger]

Michael,
I enjoyed reading you post.

I believe you are correct in the use of those valves. That has been my experience with our '87PT. Early on in ownership I found a couple valves were leaking, tightened the screws, and all has been good for about 3 years.


I'd replace the valve that you had apart. The others I would leave until it's time to replace them. Leaving things alone that are not failing is a good thing. Otherwise problems can be introduced, such as line and line-nut failures, etc.


Please keep us posted.

On Mon, Mar 3, 2008 at 9:28 AM, msksann <"msksan@gmail.com"> wrote:

Last week I took my Bird on a short 2-day shakedown run just 50 miles

outside of San Diego, far enough to reach operating temps. On arrival

at the campground, I heard a slight air leak, and crawling between the

Tag Axle and the Drive Axle, I found a device leaking air out of a

seal clamped down by 4 screws. The Pressure Protection Valve looks, to

me, like a small regulator similar to a propane regulator. Midland

part #N15759C (N157590) BB part #0522508. This has been replaced by

the Haldex KN31000, available at napa for aprox $38. Or online for less:

http://tinyurl.com/24ngm4

http://tinyurl.com/2zs6qn



Tightening the 4 screws about 1/8 of a turn stopped the leak, and

after crawling out from between the Axles, I fired up and waited until

the air drier purged at 120 psi, shut down, and crawled back under to

re-check the leak and surrounding area with soapy water, and then with

my ultrasonic leak detector. All good. Crawling back out, my

girlfriend, whose hearing is clearly better than mine is, told me she

still heard a hissing. Back underneath, everything still checked out

okay, but I did hear a leak further forward, so lying on my back, I

managed to pull my skinny body under the Drive Axle into into the next

forward compartment. This is the tightest, and scariest, place I have

contorted myself into yet! Sure enough, next to the air drier, and

loomed into a complex series of connectors, adapters, and other

unknown devices, was another Pressure Protection Valve, leaking thru

the seal just like the other PPV. Even I could not fit into this area,

right side (curb side of the air drier), but with the rear end yoke

pressing against my chest, and my left cheek (facial) resting against

the drier, looking out of the corner of my eye, I could just touch the

PPV with my fingertips. Okay, with much verbal lubrication, I managed

to tighten these screws as I did the other. Getting myself out of that

chamber as fast as I could, I re-pressurized the air system until

purge again, but this time, the air leak was even worse, and leaking

out of a small breather hole in the cap. Research time.

The PPV, with one inlet, 1 outlet, and 2 accessory connections, is

commonly used to isolate leaking air accessories from the air system.

Used as it is between the air tank, and the Ridewell air spring

suspension, only the inlet and outlet is used, with the accessory

ports plugged. I believe(?) this is what keeps the Ridwell air spring

suspension (airbags) from inflating until 65psi is reached, and closes

off if air pressure drops to 45psi. Back underneath, I managed to

remove the 4 screws, revealing a flat diaphragm, which clamped between

the two halves served as the seal, and a spring with a tiny metal cap

on the end to protect the diaphragm. Examination showed the diaphragm

was stiff with cracks throughout. Toadless, I had no problem having

NAPA deliver one to me at the campground, but being that there was no

way I could remove and replace the whole unit in it's location, it

seemed "easy" enough to just harvest the diaphragm out of a

replacement, and rebuild the original. Well, the newer replacement is

designed slightly different, with a smaller diaphragm counterset in

the center, instead of clamped…

Hmmm, the diaphragm material is .05 inches thick, and I have seen this

material before used in a Par Water Pump rebuild kit I had on a

sailboat, but is this material good to be used with air and oil? Best

research I could do shows that it is (??) A call to a friend,

confirmed the same .05" thickness, and he delivered one out to me.

With twisted spine, more verbal lube, much complaining, (and a bit of

claustrophobia), I replaced the seal/ diaphragm, and it is working

properly. I suspect all of the material in these valves are getting

hard and forming cracks, and I plan on replacing them all with new

Haldex PPV's at first opportunity. The Tag Axle PPV can be done with a

little effort, and I will also have a shop replace the Drive and Front

Axle Suspension one that I rebuilt, (to alleviate lingering worry

about the material replacement).

On the air system diagram in my blue box owners manual, (Figure 10-13.

Air System Sheet 1), they are listed as part #2. I would be interested

in any feedback the many, more experienced owners on the forum might

have regarding failure. Am I am correct in the full purpose of there

valves as used in the Ridewell air spring system?



Thanks in advance!



Michael Kramer

86 PT-40 8V92

San Diego, CA

--
Curt Sprenger
1987 PT38 8V92 "MacAttack Racing"
Anaheim Hills, CA