Galleymaid head pump Airbound

[JLR]

The VIP GM head pump has started to become airbound on the discharge side after every second or third flush. Releasing the priming plug on the discharge side releases the air and reprimes the pump and it discharges properly. The stator is relatively new ( less than one year or 30 flushes). I have a vented loop installed. Not too sure where to go from here but releasing the air after every second or third flush is not a good option. So, where is it sucking air from or what is the fix. I guess there is a possibility of something wrapped around the macerater but I do not think that would create this symptom. Also, I have not really cranked down on the small nuts that tighten the discharge bell to the housing so I guess I could be getting air in from there. After more than twenty years with GM heads on several boats, I would have thought I would have been able to fix this. Any help is appreciated.

 

[MikeP]

So the head is not emptying when you press the flush button... What happens to the liquid in the bowl when flush is pressed, does it just sit there or does the intake side of the pump keep filling the bowl with water until it would overflow if you let it?

IOW, if the exhaust is plugged/whatever, there should still be the normal amount of flush water coming into the head since the two pump sections are independent. If no water is coming into the head, there is an issue with the intake side/plumbing.

Did this just start happening recently? Was anything changed just prior to the appearance of these symptoms?

 

[JLR]

Thanks Mike. Nothing has changed. The intake side is working fine. Water fills from the intake side of the pump when the pump flush button is pressed. It keeps coming until until the button is released. Unless and until the suction discharge side of the pump picks up its prime, no water is evacuated from the bowl. Darn thing just seems to get airbound on the discharge side.

 

[MikeP]

Hmmm…

If you haven't already done so, take a look at this:

http://razmarinepumps.com/marine-toilet-head-water-pumps/raz-marine-pumps-trouble-shooting.html

 

[JLR]

Thanks. I also heard there may actually be a small clear tube that goes from the head to a PVC fitting that also serves to lube the discharge side. If so, I need to check that tube for possible air leaks. Kind of a one off question.

 

[tonytrakovich]

This happened with my old GM heads. This is not a fix, but when this happened and I needed to evacuate the bowl (you know what I mean), I found that I could momentarily depress the flush button several times (1 sec on, 1 sec off) and the pump would "catch" and flush. My heads did not have the time delay solenoids on them.

Changing the rubber pieces in the discharge side of the pump corrected this. Also as JLR mentioned, the clear tube on mine was totally clogged in the fittings. I cleaned the fittings out and the problem happened less frequently. I think this fitting lubes and primes the discharge side of the pump?

 

[MikeP]

Yes, that clear tube was added some years ago by GM in production to resolve such problems so perhaps it's clogged. GM recommended adding it to heads that did not have it.

 

[dottieshusband]

The clear tube vents air from the discharge hose through the rim water inlets. If it gets clogged, you will get air bubbles coming out of the bowl water.

 

[Nonchalant1]

That pump originally had a discharge side priming tube to prevent this problem. It was a small copper tube that ran from the threaded hole on the intake pump to the threaded hole on the discharge pump. When the pump runs a small amount of water went through the tube to prime the discharge pump in case it was blocked with air. The threaded holes are still there, with a plug, but they no longer put the tube in because if the geometry of the boat and heads is a little strange, then seawater can siphon through the tube and slowly fill the holding tank.

Two possible solutions:
1. Check to make sure that the discharge line leading away from the pump has a upward section right after the pump before it runs to the holding tank. This ensures that the last water from a discharge will keep the pump primed. It loses prime when the remaining water can run away downhill..
2. Re-install the priming line using original type copper tubing and pressure fittings. As long as water can't run from the thru-hull through the pump by itself (i.e. a high loop in the intake line above the waterline) it will not siphon.

Doug

 

[JLR]

I spoke with the folks at Razz. He says that the symptom (air in the discharge side) is consistent with having something wrapped around the macerator. While I was hoping that was not the case, if so, at least it is an easy fix to find and correct.