Aux air pump system replacement
Since we've owned our FT, I have not been impressed with the aux air pump or its configuration.
- I didn't like that it ran as long as it did.
- I didn't like that it ran as often as it did.
- I didn't like that it ran every time the HWH control tried to raise something, regardless of the pressure in the system.
- The Thomas pump was only rated for intermittent duty.
- The differential setting of the pressure switch was only 65-85psi.
To address these issues, I first did some looking at different air pumps that were available, also trying to find information as to how loud each pump was. There seems to be very little information out there as to the noise levels of these DC pumps, so I had to do a bit of digging. I was able to measure my Thomas pump, and took measurements 1' from the pump in the bay, 3' away from the coach with the basement closed, in the galley and in the bedroom. In the picture in the first reply, I also measured these spots with the new pump I chose, after installation. I did search out a local fellow with the ARB dual pump setup and measured its db 1' away, and it was 89db. The Thomas pump was 83db and the Air Zenith OB2 pump I used was 87db, so the dual ARB setup would be roughly 2db louder at all measurement points I'd suppose.
There were a few criteria that I wanted to address with my updated system:
- I wanted something with higher total pressure capability (140psi).
- I wanted something that would have an adjustable or much wider pressure differential for the control circuit (65-120psi).
- I wanted to be able to draw off the system for air needs, or add into the system from other air sources.
- I wanted to be able to completely disable the system so the pump would not run if I didn't want it to.
The system is wired with a 3-position switch. This switch can be in "Auto", "Off", or "On" modes. In the "Off" position, the pump will not run for any reason. In the "On" position, the pump will run until it reaches the pressure switch cutoff at 140psi. This switch is set to restart at 115psi, mainly for manual usage. In the "Auto" position, the pump will run during any of these situations:
- The pressure drops to 65psi, the preset restart pressure.
- The Air Tank switch is engaged inside, which sends air to the wet tank. This will run the pump as if the switch were on, being limited by the high pressure switch (140psi).
- There is a call from the HWH to raise the coach that lasts longer than 25 seconds.
I was able to reuse the original air pump mounting bracket, rotated 180*. I sandblasted it, repainted it and then added a 1/8" aluminum back plate for mounting the relays, circuit breaker and diode for the aux air switch. I then cut a "T" shape mount for the air manifold out of a piece of 1/4" aluminum plate and mounted it to the new front of the pump bracket.
The left most relay (orange) is the delay relay. When the HWH system calls to raise, it would normally run the pump. In some cases, I'd imagine there will be enough air in the system to raise the coach without the need for the noisy pump to run, so I've added a delay relay that will not start the pump for about 25 seconds after the system starts to try to raise the coach. If the HWH is still trying to raise after 25 seconds, then the pump will run.
The next relays are (from left to right):
- The primary pressure relay - will allow the pump to run when pressure is below 140psi. This regulates the pump when the switch is in the "On" position.
- "On" relay - runs the pump when the switch is on. This is also used if the Air Tank switch is flipped.
- "Auto" relay - runs the pump when the digital pressure switch commands it.
- HWH Delay relay - uses the delay relay signal to control when to run the pump.
There is a 70a circuit breaker where the main power comes from the batteries. There is a also a Blue Sea Systems dual bus bar for the power and ground needs for the systems.
On the air manifold, there is the pressure gauge at the top, the 140psi pressure switch on the right side, and the Air Tank solenoid connected to line 76. The next row down has the 150psi pressure relief valve. Next is the digital pressure switch and the line 75 out to the HWH tank and manifolds. Next is the air chuck with a check valve to be able to connect an external air source to air up this system, a female air coupler for air needs, and on the other side, line 57 goes out to the slide bladder air tank. At the bottom is the check valve from the incoming air from the filter/dryers and air pump.
So far I'm happy with the outcome, and will give it a proper test next month during our next two outings.
Primary parts list:
Air pump: Air Zenith – Air Suspensions
3-stage filter/dryer: 3 STAGE, HEAVY DUTY INDUSTRIAL GRADE FILTER REGULATOR COALESCING DESICCANT...
14-port air manifold: McMaster-Carr
140psi switch: McMaster-Carr
Digital pressure switch: McMaster-Carr
Low coil amperage mini relay: G5Q-1A4-DC12 Omron Electronics | Mouser
Delay relay, 0.6-60sec: McMaster-Carr
0-160psi 2.5" pressure gauge: MEANLIN MEASURE 0~160Psi Stainless Steel 1/4" NPT 2.5" FACE DIAL Liquid...
Primary relays: IRHAPSODY 60AMP 12VDC Relay and Harness, Heavy Duty 12 AWG Tinned Copper...
150psi safety pop-off valve: Milton S-1090-150 1/4" MNPT ASME Safety Valve - 150 PSI Pop off Pressure -...
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Topic: Aux air pump system replacement