How much vacuum(inHg) and how long should a vacuflush rebuild hold

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The Brockerts

Senior Member
Joined
Oct 17, 2014
Messages
263
Location
USA
Vessel Name
Moonstruck
Vessel Make
1990 Californian/Carver 48 MY
I've rebuilt a vacuflush pump and then tested it with a vacuum gauge. It created 20 inHg at the start but after 5 hours it was down to 13 inHg.
Do you think this will work?

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It’ll work, but it will cycle now and then. When the valves are wet it will hold better.
I’ve had them hold for days.
 
Oh yeah, I was thinking they were set at 16” vacuum.
And those push lock fittings aren’t the best for vacuum testing.
 
Draw your own conclusions from the attached, but it would seem to be not ok. However note, while I could not find a spec for what the pump should be able to pull, the “system” should be at 10”. This is regulated by the vacuum cutout switch. Your photo shows you checking vacuum right at the pump, not the VG input, so you have no protection from excessive vacuum creation. Hopefully you haven’t inverted a duckbill or otherwise damaged the pump. The fact you’ve pulled 20” of vacuum takes you outside the tables.

Suggest you remove and check the duckbills. Also, when installing them be sure to grease both sides of the “lip” of the duckbills. If not you risk deforming them as you tighten the fittings. I learned this the hard way; worst case it was “twisted” so bad it did not hold vacuum at all. But gently and properly lubricated and installed, they should be good. I was pretty anal about maintenance, and my system would hold vacuum for at least two weeks. I don’t know how long it might have - we left the boat for two weeks with the toilet breakers off, and upon returning and flipping the breakers on, the system did not cycle. So who knows ultimately how long it might have held.
 

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Or replace with Marine Elegance!
 
The EASY solution is to simply put a switch (near the toilet) on the power side of the vacuum pump. When you're ready to use the toilet, you simply turn the pump on. It cycles and creates vacuum and then when you're done, you flush and then turn off the switch. This way the darn thing isn't constantly cycling but it still works perfectly fine:)
 
Hmmm I've never tested one like that.

I would get the duckbills wet and give it a try. It should hold vacumme pretty much forever.
I have two of them and never hear them cycle except intentionally
 
Have to say - after having the vacuum flush system on two boats, I've had enough!! Next boat will be electric with a macerator! There's just GOT to be a better way! Holding a vacuum is just not natural!! LOL! Good luck!
 
"Holding a vacuum is just not natural"
Interesting thing to say. I would agree. In my engineering experience I've found it easier to keep a pressure system than a vacuum system. Weird since a complete vac would only be putting 14.7psi pressure on its components, yet we regularly manage 6000psi without a hitch.
I really liked my VacuFlush in my previous boat. Maintenance was minimal in man-hours per year. That said, if I get my new-build going one of these days then I'm designing it with Dometic RV heads bolted to the top of holding tanks --> world's best heads short of a hole in a board or a cedar bucket!
 
The old adage "nature abhors a vacuum" is proven again - :)
 
My guess here is if you had only pulled 10 you would still beat 10 a week later. By pulling to 20 you have pulled more than the system is designed for so something has distorted and started leaking under the extreme pressure.

Retest at 10 and see what happens.
 
High pressure might be deforming your duck bills. When it's right, it should hold a vacuum for a long time. Lots of places to leak, having it out like you do, you might hear the hissing of the air leak. Leaks can be hard to find. Mine ended up being the tank body, gasket was out of it's track. Will hold for at least a month now.
 
"Holding a vacuum is just not natural"
Interesting thing to say. I would agree. In my engineering experience I've found it easier to keep a pressure system than a vacuum system. Weird since a complete vac would only be putting 14.7psi pressure on its components, yet we regularly manage 6000psi without a hitch.
I really liked my VacuFlush in my previous boat. Maintenance was minimal in man-hours per year. That said, if I get my new-build going one of these days then I'm designing it with Dometic RV heads bolted to the top of holding tanks --> world's best heads short of a hole in a board or a cedar bucket!
Agree but would note pressure systems don't rely on slip fittings and duck bills.
IMO there are way too many places for leaks to occur on a VF system... give me a macerator any day!
 
The EASY solution is to simply put a switch (near the toilet) on the power side of the vacuum pump. When you're ready to use the toilet, you simply turn the pump on. It cycles and creates vacuum and then when you're done, you flush and then turn off the switch. This way the darn thing isn't constantly cycling but it still works perfectly fine:)
Exactly. Who cares if your Vacuflush can hold a vacuum for 14 weeks? (And you have tested it by turning off the circuit breaker for the whole time.) Who cares if you hot-rodded your toilet to hold an additional 2Hg over a stock Vacuflush? (And you bought a vacuum gauge just to test it.) Who cares if your Vacuflush is instantly ready to flush at a moments notice? (And you hold the world's record for expeditious defecation.) It's only a f*****ing head! (Say that in a scream for full effect.)

Not only does the switch keep the Vacuflush from cycling at night (hence the common misnomer "night switch"), it also relieves the duckbills and other gaskets of holding a vacuum for weeks, months, or years for no reason. That extends their lives by decades.

Too complex? Word on TF is, if you are being outsmarted by a Vacuflush, install a Marine Elegance.
 
Hi! My approach would be to test the vacuum when the pump is attached to the tank! I have a spare 90 deg hose fitting, as unless you’re replacing the hose from the funnel (the old hose is almost impossible to remove off the bend), a spare 90 deg bend makes troubleshooting easier. You can either use the vacuum gauge in the hose bend end or a rubber squash ball works great to hold the vacuum! Start the pump, let the vacuum switch stop it and see how long it holds vacuum.

This approach tests the complete unit including the vacuum switch, duckbills, bellows, O rings, and 90 deg bend seal!

One of my units started kicking on recently every 10 mins or so, but water was staying in the bowl, so the seal was good! Testing the complete pump/tank assembly as described above, the vacuum held overnight, so that meant the leak was either the pedal cartridge shaft (o rings) the funnel or hose. The shaft cartridge was relatively new and I had replaced the hose, so then checked the funnel. Viola… minute cracks and indentations. Replaced the funnel and problem fixed!

Hope this helps! I’ve attached a couple of pics - sorry about the center graphics - they are photos from a video. Cheers
 

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