Can anyone tell me where I can download a schematic for the air system on a 1985 Volvo F10?
I'm battling an issue with a Volvo F10. When you start to build up air pressure it leaks out of the exhaust port of the valve shown in the first photo. I don't know what this valve does. The park brake system has a reset knob in the supply line to the park brake control. When you lose air pressure, this knob pops out, and disables the park brake control, and you can't push it back in to reset it until you have built up sufficient air pressure. As I mentioned, when trying to build up air, it leaks out of the exhaust of the valve. Eventually when you get enough air pressure to push in the reset knob, the valve stops leaking out of its exhaust port, and then everything works as it should. The main problem is that it takes a long time to build up air pressure when you are losing a lot of it out of the leaking valve. The reset knob seems to me that it is working perfectly. It only has an air line in, and another air line out. It holds air until you press the knob in, then it lets it go out the outlet line. Normally when a valve is leaking I would pull it apart and see if it was sticking or had worn seals inside. But because this seems to immediately come good when you push the reset knob, it makes me wonder whether there is anything wrong with this valve at all. The park brake control has 4 air lines going to it. One is supply, from the reset knob. One is an exhaust leading out of the cabin. One has air pressure only when you move the park brake control to the release position. The other air line has pressure when the park brake is applied, and no pressure when you move it to release. So when the air pressure is low, the reset knob is out, the valve underneath is leaking, and there is no air supplied to the park brake control because the reset knob stops it. When you build up air pressure and push the reset knob, it supplies the park brake control with air, and sends air pressure down the air line which has air pressure in the park brake applied position, which stops the valve from leaking out of its exhaust. Does anybody have any ideas as to what is causing the valve to leak? Does anybody have any idea what the air line from the park brake control which has pressure in the applied position is supposed to do? Does this make sense to anybody? It is all pretty hard to explain in writing. If anybody has seen this before or has any suggestions I would appreciate it. I'm still looking for an air brake schematic so I can try to work out how this system works if anybody has any idea of where I could find one on the internet. Another question, why don't they put the drain valves on the bottom of the air tanks?
best advice i can give is perhaps try here http://www.trucknetuk.com/phpBB/ plenty of old drivers who used to and still do run them , you will have to register though
Hi there, that sounds like everything is doing what it is ment to !! Maybe the resetvalve is leaking a little, but what you described is exactly how the system works. The reset valve only pops out when the air system is low, so if it keeps popping out, you have leaks.
That's a relay valve. Basically it sits between an air receiver and brake actuators(s) and allows a short path and big air lines to quickly move the actuators without having to push the air all the way up to the cab, through a valve and back down again. When the air in the actuator is no longer needed, it is dumped through the rubber disc you're indicating. The only time air should be coming out of it is either when a park brake is being applied or a service brake is being released. If you've got air leaking from it all the time, that's your problem. Either strip/clean or R&R. Good luck.
Thankyou for the replies, I don't think the relay valve underneath leaking air is "doing what it is meant to" As I stated, the reset valve is working fine. It is not leaking. It pops out when air pressure gets low. Yes I have leaks. The truck is 30 years old. It's just a matter of fixing the worst ones. The air doesn't leak from it all the time. It only leaks when the reset knob is out. As soon as you push the reset knob in, the relay valve stops leaking, and the system works like it is supposed to. Therefore is there any point me stripping and cleaning it or replacing it if it doesn't leak all of the time? I would like to know what purpose the air line from the park brake control which has air pressure when the park brake is applied is meant to do, if anyone has any idea. It may be similar to systems on other European trucks. Whatever this air line does seems related to the relay valve. Here is a chain of events - the relay valve is leaking, you push the reset knob in which supplies the park brake control (still in applied position) with air and as a result the air line in question becomes pressurised and at the same time the relay valve stops leaking. I can understand what the other outlet air line is for, which is pressurised when the park brake control is in the release position, but not this one which is pressurised in the applied position.
OK i can try to explain how it works. The control knob poops out when the pressure is to low. Load air and when passing the limit you aply it and can take of the park brake. Taking it of gives you pressure out on the brakes. Applying park brake, drains the pressure to the park brake. The knob makes it impossible to release the parkbrake, without enough pressure to use the "normal" brakes. And here comes a tip about the pressure line you are asking about: If you aply the park brake, AND pull out the reset knob, you have to pull for some time to leak out the pressure. Then the brakes go on on all wheels, including on the trailer. Aka pulling it out aplies alle brakes on all wheels. If i understand what u explaine, it is a pressure line linked to the main brakevalve. This line controls the effect i talk about when u drain the safety valve to get full brakes on all wheels. I use this function all the time when i load equipment on our equipmenttrailers. The trailer stands rock solid when loading heavy stuff on the trailer.(just be patient with the knob and drain the air) There is only on axle with spring brakes on the trailers... Another question, you keep the park handle in applied position when you try to load air? I have a feeling, if not, the system tryes to apply full brakes on all wheels, before loading the main/primary pressure. Thats maybee the reason for the draining of the valve..
MKTEF - Thankyou very much for this. I now have some info about how the system works. It will be a great help. Thanks again.
It turns out it is a trailer control relay valve of some sort. When the system is low on air (reset knob popped out) the system applies the trailer brakes, like MKTEF said, and the valve leaks. I found that the valve also leaks when pulling the trailer brake lever. It only would leak when the trailer brakes were applied, which is why it would seem to come good when the system built up pressure and I pushed in the reset knob. I dismantled the leaking valve, cleaned it out, fitted a few new O-rings and filed down the rubber seat of the flat main seal inside and re-assembled. The problem is fixed. Thanks for the suggestions. Now, the other part of my question, does anybody have any idea of why they put a drain valve on an air tank but not at the bottom of the tank, like I show in the photo? There has to be a couple of inches of sludge in the bottom of the tank before any will drain out of the valve.
Regarding the drainige its related to the production of the tanks. Its easier for them to put them on the end. And they are bether sheilded on the end. When u drain i think the airflow will draw all the water out of the tanks, even if the vale is not at the bottom of the tank. I know from Scania, who has the valve at the bottom, that the valves often leaked. And thats because the sludge and rust ended in the valve making problems with it.
I've also seen air tanks where the tank itself was inclined slightly and the drain at the end was located right where the water will run to if the truck is parked on flat ground. Last time I ran an F10 was 1990. Damn good truck and pretty well unbreakable. God it seems like only yesterday, and I can still remember the licence number. How sad does that make me ..?