air tank pressure protection valves

[David Little]

 My 1995 Beaver Patriot on a Spartan chassis has a pressure protection valve between the primary and secondary air tanks. The wet tank is the top tank and is fed by the engine compressor. Once that tank reaches a certain pressure, the pressure protection valve opens, and air feeds into the secondary bottom air tank. If pressure get too low in the secondary tank, ( a blown air bag, etc.) the valve will shut and trap the air in the top tank, (Primary, rear brakes). My valve is leaking badly out of the vent holes on the bottom and around the joint of the two halves. The diaphragm is shot. I have to replace it. Problem is, I do not know what the original pressure to OPEN the valve is, and what the SHUT pressure is. the numbers on the valve are N15759DD.  I can find many valves with that number, but they are set to open at 95 PSI and close at 90 PSI. I see other ratings for open at 65 and close at 45. I bench tested the valve and it seem to start to open at about 60 PSI. It is leaking so bad that I do not trust the bench test for open or close pressures. I called Spartan and they are useless on this matter. Does anyone have any idea at what pressure the OEM valve was set to open, and close at?  It is a simple two tank system, full air brakes, (drum brakes) all around with 4 air bags.

[Eric Maclean Co-Admin]

David
I'm not sure about your tank configuration but if you only have two tanks then the first tank is most certainty a dual tank meaning it looks like a signal tank
But it has a divider baffle in the center with a check valve in it making the first half your wet tank and the second half the primary tank .
After 1972  air brake systems by federal law were required to have two separate air feeds to a dual air brake treadle valve so you effectively have two separate brake systems ( front and rear ).  For safety reasons if one system lost all its pressure you would still have the second to bring the vehicle to a stop.
With the two tanks the second one is the secondary tank not an accessory tank the valve you are seeing is the primary tank brake protection valve which accomplishes the protection feature between the primary and secondary tanks. So in the event of catastrophic pressure lost on either tank the valve would stop the remaining air in the non effected tank from transferring and escaping leaving you with not brake air pressure.
This is why those air pressures seam high to you that valve is set higher to maintain enough air pressure to effectively operate the remaining or no effected brake system.
That valve is speed to open at 95psi and close at 75psi

The air pressures you have on that valve are correct for that application, again this is a brake protection valve not an accessory protection valve.

With that said you should also find an accessory protection valve on the secondary tank leading off to run the accessories such as air bags ,air doors ,HVAC etc this protection valve will have the lower air pressures your mentioned as it's job is to protect and maintain the secondary tank air pressure above a minimum air pressure for proper air brake operation usually closing at  70 to 75 psi which is enough to operate the second set of brakes usually the front
The two different cut off pressures are what differentiate the primary and secondary . Usually the primary system operates the larger drive axle brakes and the secondary provides air for the secondary ( front) brakes and accessories.

https://www.fleet-products.ca/kn31010-g-95-75-psi-inline-pressure-protection-valve-n15759dd-90555396/?srsltid=AYCX9vJuWrF8EF2Dyqn8-5lk59Y3FosQ3Yr4BlotiecYIfZM8MV8LZ15


Hope this helps
Eric

[David Little]

Thank you, Eric. You certainly gave a fantastic description on the air tanks and equipment.  I have also done much more research after I found leaks on both pressure protection valves on my Beaver. The one you gave a link to (KN3101-G) is extinct. No vendor can fine one after many calls. That pressure protection valve fits in between the primary tank and secondary tank. The 95 PSI open and 75 PSI shut would have been great. I installed and tried a Haldex 90555396 valve that has a 70 PSI open and a 65 PSI close. NO good. What happens with valve is it starts to squeal loudly once the primary tank hits 70 PSI and begins to fill the secondary tank. It sounds like an air horn and last until the secondary tank reaches 70 PSI. The valve seat is chattering hundreds of times a second to make the air horn noise. So that is a FAIL as the seat would wear out pre-maturely. Cleaning up the original OEM valve that Spartan installed I found a part number stamped on it. The number on that OEM valve is N15759DD. The "DD" in the part number designates that it opens at 95 PSI. There are several for sale that end in "DC" and they open at 65 PSI and close at 45 PSI. I thought the 45 PSI would be too low, so I did not buy that one.  The N15759DD was made in the 1990's by Midland. It has an opening pressure of 95 PSI and a closing pressure of about 83 PSI according the vintage Haldex/Midland spec sheet I found that even had a picture of my exact valve on it. So Haldex bought Midland at some point and now sells the comparable valve as the KN31010. It is also a different casting and shape than the Haldex KN31010-G and the Haldex 90555396 that I tried. It is the same exact shape as my original, which made no "air horn noise" when working to fill the secondary tank. I think the orifice in the 90555396 was too small and caused the Train horn effect. So, the KN31010 is the one I will try next. It opens at 95 and closes at about 83 PSI, just like the original. It is on order.  As far as the other pressure protection valve on the secondary tank, it screws into a port and only feeds the air bag system. Nothing else. IF an air bag blows, it will shut off and save the Air pressure in the secondary tanks so that the front brakes still work, as they feed of a port on the secondary tank with no protection valve at all. The original valve on my 1995 Patriot was a Neway 90554107. Haldex still makes that exact valve after they bought out Neway and it is now a Haldex 90554107 valve. It opens at 75 PSI and closes at 70 PSI.  It is widely available with many genuine Haldex made in USA on eBay for about $45. As of note, there are also many China made knock offs of both valves for about half price. I will not run a China made Valve for the brake and air bag system on my Beaver, ever! I have the Haldex 90554107 on order as well. By the way, I used a leak detector fluid (much like soap and water) and sprayed both original valves.  Many bubbles came out of each old valve. No wonder my coach would lose all my air pressure in about 6 hours! I will report back on how the new valves work once installed, and how long my air pressure holds up as compared to the 6 hours the leaking valves gave me. Hope this helps somebody, David