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Topic: Replacing the aux compressor and HWH pressure requirements (Read 1241 times) previous topic - next topic

Replacing the aux compressor and HWH pressure requirements

The aux compressor in my coach is the Thomas TA-4101-DC.  The specs are:
    • 12V DC, 28 amps max
    • 100psi max rated, although I've seen it go to 120psi trying to raise the coach.
    • 2.2CFM free flow, 0.95 @ 100psi
    • It's not quiet...registered 82db on my meter about a foot away, and 55db about a foot outside of the compartment with the bay door closed.

Best I can figure, the HWH tank up front is about 6 gallons (looks to be 8" diameter x 28" long).  Between somewhat low volume and the pressure regulator set to bring the compressor on at about 65psi and shut off about 85psi, it runs way too often for my taste.

My first thought was to change the pressure settings...if it built more pressure in the tank, it would take longer to get back to the pressure limit to start the compressor.  Thomas' specs say 100psi max though, so maybe not a great idea with this compressor.  Not to mention, the flow is only 0.95CFM @ 100psi.

My next thought was how about adding another tank to increase the volume of the system.  More volume means more time before the pressure drops and the pump needs to run again, but this also means it needs to run longer when it runs.

That brings up the last option - replacing the pump.  I've looked at quite a few and compared specs.  The harder thing to come up with is a noise level for these pumps.  The ARB dual pump specs are:
    • 12V DC, 69amps max
    • 150psi max rated
    • 6.16CFM free flow, 3.0CFM @ 90psi.  This is 3 times what the Thomas pump will do at 90psi, so it would be 3x faster.
    • Found someone local and measured this pump at 89.5db from about a foot away.  Quite a bit more noise than the Thomas and more than the Air Zenith.

This is 3 times what the Thomas pump will do at 90psi, so it would be 3x faster.

I also looked at the Air Zenith OB2.  Specs are:
    • 12V DC, 32amps max
    • 200psi max rated
    • 4.25CFM free flow, 2.66CFM @ 90psi.  This is 2.8x what the Thomas pump will move at 90psi.
    • 86db at about a foot away according to a YouTube video I found reviewing it.

Seems like this one is about 4db louder than my Thomas pump.  Based on the specs on their website, it appears it should be able to fill my 6 gallon HWH tank from 60psi to 100psi in about 63 seconds.  That's way ahead of how long it takes for the current pump.

My questions are, has anyone played with the pressure range that the HWH system/tank runs at?  Any reason not to run it up into the 120psi range, to allow for more time between pump activations?  I've seen the current system get that high when trying to manually raise the coach from the HWH panel, so it seems it will go there without issues.

Has anyone used the Air Zenith pump and if so, what are your impressions?  What other pumps have been used, how did you/do you like it and has anyone measured the noise level when it is running to compare to the OEM?
Keith
2003 U320 38' #6197

Re: Replacing the aux compressor and HWH pressure requirements

Reply #1 –
If you raise the pressure setting on the stock pump, the effect is similar to adding another tank.  Pump may run less often but when it does cut on it will run for a longer time.

So your choice either way is more frequent shorter run times, or less frequent longer run times.  Which is more (or less) desirable (to you)?

I think Don (Don & Tys) has (or had) one of the ARB pumps on his coach.  He may comment on the noise factor.

What is the purpose of this HWH Tank Solenoid?


1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Replacing the aux compressor and HWH pressure requirements

Reply #2 –
I replaced the sticking pressure switch in my coach and the one FT sold me (same number as the original one) has a nominal cut off of 100 psi.  I had replaced the small compressor (1/10 hp) with a bigger Thomas (1/3 hp).  It never actually got pressure in the HWH tank to 100 so I adjusted the pressure valve until the HWH tank reads a bit over 100 when the compressor shuts off.  In my coach I need about 90 psi to adjust level.  Less than that won't do it in any reasonable time if at all.

The pump will run if it has power and the pressure switch hits the low limit or when the HWH leveling system calls for air no matter what the pressure in the HWH tank is. The HWH system calls for air when the level system is left in automatic mode when ever it wants to raise any part of the coach.  In manual mode, it will call for air and turn on the compressor any time you want to raise any part of the coach.

The HWH tank holds air for operation the slide seal bladders. Check valves (if they are working) isolate it from the leveling system.  Deflating the bladders uses compressed air from the tank (and the compressor) to create the vacuum that sucks air from the bladder. It also supplies the compressed air that reinflates them. The air in the tank provides the compressed air to keep the seal inflated to about 15 psi as well.

I have an ARB compressor too that is installed but the plumbing is not complete.  It will be plumbed (when we get home) so that it will be a backup for the Thomas compressor, work in parallel at the sme time as the Thomas compressor or run on its own as an aux air source.

Neither compressor is quiet. They only run when I turn them on, the level,aystem always gets left in manual mode.
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Replacing the aux compressor and HWH pressure requirements

Reply #3 –
I helped the compressor noise by unbolting it from the angle iron frame and putting a couple of layers of closed cell foam under the 4 feet then securing it with heavy cable ties through the bolt holes. About 80% noise reduction from inside the coach.

Jim

2002 U320 42'
Jim Frerichs
2002 U320 42'

Re: Replacing the aux compressor and HWH pressure requirements

Reply #4 –
Quote from: WS6_Keith –
What other pumps have been used, how did you/do you like it and has anyone measured the noise level when it is running to compare to the OEM?
I have a single Viair 38002. 22amps/100psi. It's not loud enough to interrupt work calls or conversations within the coach but loud enough to wake me during the night. It's certainly enough to motivate me to find air leaks. I can measure it for you when I take it off the safety stands if you want, but I doubt it's any better.

You can see in the pictures that I added dynamat knock-off to the roof of the bay and the door. It made virtually zero difference inside the coach but a noticeable difference when standing outside.

You should talk to Woody. Whatever he has in his coach is dead silent...it gave me some serious envy when we were at Q together.
1987 Grand Villa ORED
2001 U320 4010

Not all that wander are lost... but I often am.

Re: Replacing the aux compressor and HWH pressure requirements

Reply #5 –
Before I move forward with a different pump, I wanted to see what I could do in regards to a wider pressure window for the existing pump.  I'm not having much luck with finding a pressure switch with a wider differential.  Most are 15-25psi.  Is anyone aware of something that will go 50-100 or 60-120?

I did find this adjustable one, but it's not cheap.  $150 + a special cable $10 + shipping.  Looks like I could do anything I want with it though.

http://www.automation24.com/electronic-pressure-switch-ifm-efector-pk6224
Keith
2003 U320 38' #6197

Re: Replacing the aux compressor and HWH pressure requirements

Reply #6 –
I was able to find someone local with the ARB twin pump setup and measured the noise today.  89.5db...quite a bit louder than the Thomas and more than the AZ pump.  It's looking more and more like a AZ pump will be in my future.

After a bit more online searching, I found this digital pressure switch where you can set the start and stop pressures to whatever you want, and it's about 1/2 the price of the first one I found.

McMaster-Carr

Since both the ARB and AZ pumps will make 1.5-2x the pressure of the Thomas pump, I've decided that when I go with a replacement, I will also want a max pressure switch in place too.  When you press the raise button, the pump is always commanded to run, regardless of the pressure in the tank, so this will stop the pump if the pressure gets to this point (140psi) and a raise command is still being sent.  This way the entire system will never exceed 140psi.

McMaster-Carr

Keith
2003 U320 38' #6197

Re: Replacing the aux compressor and HWH pressure requirements

Reply #7 –
Pre-weekend update.  I bought the two pressure sensors mentioned in my previous post, and the Air Zenith OB2 compressor.  I don't think I have every fitting I need to complete the install this weekend, but I have most of it.  I'll start a new thread about the swap with measurements, pictures, etc and link it in here.
Keith
2003 U320 38' #6197

Re: Replacing the aux compressor and HWH pressure requirements

Reply #8 –
Update:  New thread about the replacement install here:  Aux air pump system replacement
Keith
2003 U320 38' #6197