Heating Valves -- What do they Control?

I recently discovered two heating system valves that were leaking. They were screw type vales, like the 2 remaining, and I replaced them with ball valves. I have 4 valves that are visible and am not sure what each controls. They are pointed to with blue arrows. 2 are pointed to but shown in the next photo. The hoses are a bit difficult to trace. I know that the lines go to the Webasco diesel heater and the engine and who knows were else. There is also a round black device (red arrow) in line with a T fitting and 2 other fittings. What is it and what does it do?

Hi Gil. On mine, I have a valve which goes to the hot water heater. It is a seperate loop.

Hello Gil J,

The 2 garden faucet style valves are definitely Prevost. The will be soldered into 1" (+-) copper pipe.

They are both off of the engine coolant and run to the dash heater core, similar to car. If you have Prevost Over-the-road heat and AC they will run through that core as well.

The core is located in the lower dash, roughly at the passengers feet and has the AC core on top and a duel cage blower underneath.

These 2 valve shut off or open hot coolant to the dash heater core. One valve, I think the upper, is for supply and the other is for return. The related piping runs forward and back in between the frame rails in what would be the ceiling of the bays, to behind the front bumper.

At the front bumper area (on your back looking straight up) is the "hot water valve" or liquid solenoid, that is activated by the heat switch at the dash. If heat is called for the valve under the bumper will open and direct coolant to the core in the dash. If heat is off, the coolant is by-passed straight back to the engine.

The valves in question isolate the forward flow to the engine area only.

Most customers leave these valves open, unless the solenoid under the front bumper is stuck open, or the diaphragm is torn, and the dash area is unintentionally receiving heat. In which case you can stop the flow by closing one or both of the garden type vales in back.

The ball valves are hard to tell without tracing, but to the water heaters as noted above sure sounds right.

Hope that helps,

Pat Sprenger
Coach Pro LLC
800-918-7172

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Originally Posted by Gil_J

I recently discovered two heating system valves that were leaking. They were screw type vales, like the 2 remaining, and I replaced them with ball valves. I have 4 valves that are visible and am not sure what each controls. They are pointed to with blue arrows. 2 are pointed to but shown in the next photo. The hoses are a bit difficult to trace. I know that the lines go to the Webasco diesel heater and the engine and who knows were else. There is also a round black device (red arrow) in line with a T fitting and 2 other fittings. What is it and what does it do?

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Gil,
The red arrow points to a temperature controlled engine coolant bypass for the Wabasto heated coolant. The device, don't remember the name, is intended to keep heated coolant from the Wabasto from circulating in the engine until the water has heated to a certain point. The intent is to heat up the cabin heaters first, then the valve will slowly open and allow water warm coolant to circulate into the engine.

So if you want to heat up the engine coolant for cold starting, you will need to run the Wabasto for an hour or so. That is what I do.

Hector

Pat and Hector, thanks!

I did a little more looking and discovered 3 engine coolant connections. The one on the front of the engine head (same as coach's front) goes to the lower faucet type valve. There's another connected to a port in the middle of the head. The last connected low on the rear of the engine, likely off the water pump. All engine connections are on the road side. The one on the lower rear of the engine does eventually connect to copper pipe. I really need to get underneath to better trace trace these. For what it's worth the two new ball valves replaced faucet valves identical to those in the copper pipes.

Thanks again,