Another Vac-U-Flush Question

My rear Vac-U-Flush pump keeps runinng, presumably not building up enough vacuum to satisify the cut out switch. Going through the trouble-shooting tips I checked all hose clamps and could not hear any hissing sound. The bowl does not leak water through the ball so the next step is to change the duck bill valves (joker valves).
There are 4 of these rubber valves 2 on the inlet and 2 on the outlet side of the pump. Problem is I could only find 2 valves. We're cruising and the supplier only had 2 and I don't want to wait a week here to get the other 2.
So given a choice which side of the pump do I choose or perhaps one on each side??

Could be either side is bad and have the same results. I would pull both sides apart to see if there is an obvious problem. Barring an obvious problem, I would put one new one on each side for a short term solution.

edit: Probably both sides are leaking if the vacuum leak is coming through the valves. Would still replace one on both sides until more can be sourced.

Ted

Inlet side only did it for me. As Ted suggests a pull apart may reveal something - to remove if you've had guests recently? Do you use single ply?

First, try running a bunch of water through the system; that's often enough to clear something that may be keeping a valve open. Then try Bill's shaving cream trick as the hissing could be quite subtle or non-existent.

Ho long has it been since they were changed? If you get to the point of going after duckbills, start with the ones on the upstream side. Do a visual to see if gapped when closed. If the look tight like the new ones, leave alone and look at the aft ones.

Where are you now? These are usually available at any marine store.

Thanks Guys. I got it fixed. I replaced the 2 outer valves and that did the trick. Not sure when I'm going to get around to the other 2. Probably when it starts leaking again

Hopefully I've got the gemlins out. We've been on the boat 2 weeks and I've replaced 2 fuel lines due to leaks, fixed a fresh water leak at a connection, fixed a generator oil leak due a small piece of paper towel wedged between the oil filter gasket and it's mating surface on the block and now this toilet issue. Whew, time for a beer.

If the ONLY problem is, the pump never cuts off...it has plenty of vacuum to flush...the most likely culprit is a failed vacuum tank switch. It has a sensor in it that turns the pump on when vacuum is lost (flushing or an air leak), off when it's achieved sufficient vacuum. The vacuum switch is a easy replacement, but a bit pricy. Meanwhile, you'll have to just turn it on and off at the breaker...which hopefully includes a "night switch" in the head so you won't have to go to the main breaker panel every time someone needs to use the toilet.

If vacuum IS low, replace the duckbills..in fact, if they haven't been replaced in at least two years, replace 'em anyway as preventive maintenance. You say that your pump only has two instead of the prescribed 4. It's possible that your pump is actually a T-Series (overboard discharge) pump instead of an S-Pump vacuum pump. They're identical except for the number of duckbills--the T-Pump only has two--one on each side--the S-Pump has 4--2 in, 2 out--and the price...the T-Pump costs about half the price of an S-pump. If your system is an older one or was an owner DIY install, it's not uncommon for owners to buy the T-Pump instead.

You'll know which it is by the number of valve nipples on each side of the pump...if there's only one, it's a T-Pump. The good news, it works just as well as the S-Pump...just requires a little more frequent duckbill replacement.

You can't just add another valve nipple to each side of a T-Pump..SeaLand made that impossible by reverse threading the nipples on it.

Now get ready for the water pump impellers!

Thanks Peggy, it's an S series pump. I could only get 2 duck bills so decided to replace the two outer ones- inlet and outlet and that did the trick. Pumps shuts off and holds vacuum.

Won't even try replacing impellers again!

Impellers are easy... First determine which way they rotate, smear some grease on the edges of the vanes and the inside of the housing...then, rotate the impeller to make the vanes bend in the right direction as you push it into the housing...tip it a bit to get the first ones in, the rest will follow if you're patient. Problems are usually caused by fighting with it instead of working with it.

I am no help here but every time I read one of these discussions on Vac U Flush problems I am happy to have a Tecma toilet. Duck bills, vacuum switches, vacuum pumps, ball valve seals, just too much stuff. With Tecma you push a button, the high speed pump in the base of the toilet fires up and sends the contents to the holding tank. Just in case my toilets ever fail I purchased an entire pump assemble for $350 as a spare.

I think the reason we see so many vac-u-flush questions is because so many people have them. My boat is 17 yo, I've owned it 5 years and this is the first time I've ever done anything to them and probably anyone has.

Our Tecmas are 13 years old and the only time it has been touched was because a washcloth fell in during a flush. Tore it down, remove wash cloth and she worked fine.