Vacuum Pump maintenance

[Four Suns]

Actually, I went and looked at the manual for the holding tank and it all Dometic tanks now have a "tanksaver" relief valve on the top of them. Some sort of ISO standard to provide 1 1/2" venting in case a vacuum is introduced into the holding tank. Looks like this:

Mine is top dead center on the tank.

You may want to get an extra few of those with that "lets introduce a vacuum in the holding tank" program. In fact, you'll probably want to plug that pesky little thing up because what the hell does the manufacturer and ISO know... they obviously don't understand fluid dynamics. I think a big wooden plug pounded in with a hammer would work just fine.

 

[mistercomputerman]

Hey Wingess,

I'm not sure I'd get into an argument over fluid dynamics with a guy who has a Master's in Aerodynamics specializing in CFD...and that's from another guy with a Master's in Aerodynamics...I'll leave it to you to figure out what CFD is...

Doesn't CFD stand for Computational
FLUID DYNAMICS

 

[electricaldoctor]

You should use a plunger with ice cubes.

Instead of ice cubes & a plunger, how about substituting a broom with some eggs?? Egg trick

enjoy ~ Ken

 

[Converse48]

I think the wingless approach is an excellent idea.
I know someone who has some experience with it.

My Dad was pumping out the tank is his boat and he didn't realize that the vent line was clogged with spider $hit. Turns out, the vaccuum imploded the holding tank. They had to tear apart the cabin sole and some cabinetry to get to it. When they found was a distorted, mangled mess. I don't recall what exact material it was, but it was some sort of metal.

The good news is he got a brand new holding tank, a new cabin sole in the master stateroom and some new cabinetry. All for the low, low price of $5,000.

 

[CJ Martin]

Tim, how dare you confront another users "theory" with actual data. Shameful! And this must be against the rules! I'd post a link to the rules, but I'm not nearly smug...er smart enough to know how.

-CJ

 

[earthmover17]

Gary,
Where did you get your duckbill parts? My guest head is starting to run a little longer. The head holds water so it's the Duckbills I'm going to first.
I hope some posters don't p!ss you off enough to drive you away. You are truly an asset.
Thanks Jack

 

[Four Suns]

I get my stuff from these guys:

http://www.sealandservices.com/vacuflush_parts.htm

Someone posted a link to

http://northeastsanitation.com/

and they look like a good outfit as well...

 

[wingless]

I think the wingless approach is an excellent idea.
I know someone who has some experience with it.

My Dad was pumping out the tank is his boat and he didn't realize that the vent line was clogged with spider $hit. Turns out, the vaccuum imploded the holding tank. They had to tear apart the cabin sole and some cabinetry to get to it. When they found was a distorted, mangled mess. I don't recall what exact material it was, but it was some sort of metal.

The good news is he got a brand new holding tank, a new cabin sole in the master stateroom and some new cabinetry. All for the low, low price of $5,000.

Thanks for the info. I'm trying to fill in the blanks.

Based on the info it sounds like the head wasn't developing vacuum. It also sounds like the holding tank was empty or almost empty.

My guess is the vacuum pump was running, but the obstructed vent was preventing vacuum from building. Is that also correct?

So the diagnosis was that pumping out an empty tank would fix the problem?

Was the head flush open or closed?

This sounds identical to my suggestion for the next stage of repair, if a plunger didn't work. That is a full holding tank and an open head flush valve. (At least the plugged vent is the same.)

So far there are two proven solutions for a failed vacu-flush system. One is to disassemble lines full of human waste and the other is to use a plunger.

There is also the one proposed solution.

Are there any other proven or proposed solutions for fixing a failed vacu-flush system?

 

[SR400DB]

Are there any other proposed solutions for fixing a failed vacu-flush system?

Yeah, the opposite of 50% of your suggestions. I have seen the plunger approach cause more problems than they have ever solved. However, Gary's solution has always proven to be a success for me.

 

[carterchapman]

Doesn't CFD stand for Computational
FLUID DYNAMICS

Bingo! We have a winner - no more calls please!

 

[fc3]

Several years ago, Just Ducky's VacuFlush system's wouldn't pull a vacuum. Instead of disassembling the vacuum pump, I turned off the fresh water pump, turned on the Vacuflush system, propped open flush valve on the head, connected the marina's pump out hose to the deck plate and, while watching the holding tank to ensure it didn't deform, intermittently plugged the vent with my finger for a second or two. After two or three cycles, the system was clear.

It worked OK for me twice.

Best regards,
Frank

Your mileage may vary. See dealer for offer specifics. Not available in all states. Void where prohibited by law.

 

[wingless]

Several years ago, Just Ducky's VacuFlush system's wouldn't pull a vacuum. Instead of disassembling the vacuum pump, I turned off the fresh water pump, turned on the Vacuflush system, propped open flush valve on the head, connected the marina's pump out hose to the deck plate and, while watching the holding tank to ensure it didn't deform, intermittently plugged the vent with my finger for a second or two. After two or three cycles, the system was clear.

It worked OK for me twice.

No shirt for you.

So there are now three proven methods for fixing vacu-flush systems: picking out poop and 'pons w/ fingers; a plunger and using a dock pump out.

 

[Four Suns]

CSR is in need of a pumpout.

 

[wingless]

Instead of disassembling the vacuum pump, I turned off the fresh water pump, turned on the Vacuflush system, propped open flush valve on the head, connected the marina's pump out hose to the deck plate and, while watching the holding tank to ensure it didn't deform, intermittently plugged the vent with my finger for a second or two.

...

It worked OK for me twice.

Before the third time you may wish to consider implementing one of my cool mods.

The holding tank level indicator switches would have random intermittent operation on the indicator lamps on my boat. The fault was crud obstructing movement of the float switches.

The factory built my boat with the switch assembly hard-wired into the wiring harness.

I modified the harness to add an in-line connector.

The connector permits me to unscrew the level switch assembly from the tanks and remove that from the boat for cleaning.

The large opening at the top of the tank would permit filling the tank prior to your next pump out station repair of your failed vacu-flush system.

The tank full of water would provide protection for the tank from vacuum collapse.

The other benefit from this cool mod is it permits access to clean the tank interior. I use this prior to winter storage.

 

[The Bill Collector]

Before the third time you may wish to consider implementing one of my cool mods.

The holding tank level indicator switches would have random intermittent operation on the indicator lamps on my boat. The fault was crud obstructing movement of the float switches.

The factory built my boat with the switch assembly hard-wired into the wiring harness.

I modified the harness to add an in-line connector.

The connector permits me to unscrew the level switch assembly from the tanks and remove that from the boat for cleaning.

The large opening at the top of the tank would permit filling the tank prior to your next pump out station repair of your failed vacu-flush system.

The tank full of water would provide protection for the tank from vacuum collapse.

The other benefit from this cool mod is it permits access to clean the tank interior. I use this prior to winter storage.

Wingless you are full of it.... "cool mods" that is....

 

[Four Suns]

Seeing as my understanding of fluid dynamics is lacking, I read a book on it last night.

Here's the danger with introducing a vacuum in the holding tank. The pump out actually removes fluid from the bottom of the tank. The pressure for the air portion is about 30 in Hg (I'm rounding up to make the math easy).

There is a vent on the top of the tank so air can enter the tank as the fluid is pumped out.

Now... we are going to plug the vents and make the holding tank a vacuum tank. Just as a reference, the small vacuum tank on a vacuflush sucks water out until the vacuum reaches 10 in Hg. Now, in our example of turning the holding tank into a vacuum tank, how much fluid (i.e. raw sewage) has to be removed?

Wow... to get the holding tank to 10 in Hg (the same pressure as the small vacuflush holding tank we are trying to bypass/simulate), we now have a tank 3/4 filled with low pressure air. That seems like a DISASTER waiting to happen. IMPLOSION!

Now you got a mess on your hands....

The other thing is this... the larger the tank, the more susceptible to imploding it will be due to the bigger flat sides. A small tank (like the vacuum tank) can handle vacuum better.

I think Mr. wingless assumes that the air is being sucked out the top so the fluid level doesn't move but that's not how these things work.

You also risk damaging components like the discharge pump (if you have this). Unlike Mr. wingloss' statement that the small stub between the discharge pump and the thru-hull won't matter, that is not the case. Between the discharge pump and the thru hull there is a vent loop that goes from the discharge pump up above the water line then back down to the thru hull. There is going to be air between the top of the hose/vent loop and the exit of the discharge pump. When you create a vacuum on the WRONG side of the single duckbill valve design, you risk having the duckbills reverse because the air expands and has to go the wrong way.. the discharge pump has a single duckbill design unlike the vacuum pump that has a dual duckbill design to handle the vacuum of 10 in Hg.

Well... that's what my understanding is... from the book I read...

I hope nobody listens to wing's hairbrained advice but I think everyone understands that....

Frank may have done it... but Frank also starts his charcoal with gasoline, drives a PWC at 80 mph, drives in Jersey, and jumps out of airplanes... not something recommended for everyone.

I have a large holding tank (I think it's 80 gallons or so) and there is no way in hell I would introduce ANY vacuum in it as I don't want a big mess on my hands.

Why doesn't someone call Domitec/Sealand and see what there view is on plugging vents and putting a vacuum in the main holding tank... I'd love to hear their response...

 

[wingless]

Here's the danger with introducing a vacuum in the holding tank.

How will a vacuum be introduced in a full tank, per my recommendations?

You also risk damaging components like the discharge pump (if you have this). Unlike Mr. wingloss' statement that the small stub between the discharge pump and the thru-hull won't matter

Where did I say that? Again, reading isn’t your strong point, is it?

When you create a vacuum on the WRONG side of the single duckbill valve design, you risk having the duckbills reverse because the air expands and has to go the wrong way.

What wrong side?

Don’t you understand how the system works?

The pump diaphragm goes up and down, creating vacuum on one set of duck bill valves and pressure on the other set. A vacuum established by the dock pump out puts CORRECT direction vacuum on the duck bill valves.

Well... that's what my understanding is... from the book I read.

Good try. Keep reading.

I hope nobody listens to wing's hairbrained advice but I think everyone understands that....

How is it acceptable for Four Suns to characterize me as “hairbrained”?


Again, is the only solution for a failed vacu-flush system, that is endorsed by Four Suns, is that closed system full of human waste should be opened and poop and ‘pons be picked out by hands?

Please, please, please follow this advice AND TAKE PICTURES!

 

[Four Suns]

OK. So if the tank is COMPLETELY full and no air in it, as the volume of fluid is extracted from the holding tank via the pump out, you assume that the volume is replaced by coming upstream from the toilet. Why do you assume that? Maybe the volume of the holding tank decreases (i.e. the tank starts to deform inward and implode) instead of the flow coming in from the blockage. The tank has to deform... It is just a question of how much and if permanent damage occurs before the blockage clears (if it does at all). If you have "something" (like a tampon) wedged in a duckbill, how much fluid has to be removed from the holding tank and how much deformation occurs before it breaks free? You know how much? I don't. What if it doesn't break free? How much deformation of the holding tank is "acceptable"? That is what you are telling people to do here. "Pump fluid out of the full holding tank which will cause the sides of the holding tank to deform inwards creating negative pressure that will pull the blockage out." That is HAIR-BRAINED ADVICE (note that "hair-brained" is being used as a compound adjective to describe the said advice and not a person).

What I'm endorsing is not damaging a system... What you propose is dangerous... especially for larger holding tanks.

I do understand how a discharge pump works. There is not a "set" of duckbill valves on each side of the bellows. There is only one unlike the vacuum pump that has two on each side. A discharge pump is not designed to hold a vacuum. it is designed to move fluid that is all near the same pressure on both sides. You ever had one apart and looked at it?

I'm pretty sure this book I read is right... water/liquid is generally incompressible so if you remove it from a vessel, the air inside the vessel will expand (because it is compressible) or if there is no air inside the vessel, the volume of the vessel will have to decrease (i.e. deform inwards).

The other issue is this... duckbills don't last forever. The rubber loses its elasticity after awhile and will not close and create a seal and so you end up without a vacuum in the vacuum tank... symptoms are constant/frequent/longer running... The things just need to be replaced from time to time and toilet plunger doesn't fix worn duckbills.

 

[fc3]

Seeing as my understanding of fluid dynamics is lacking, I read a book on it last night.

Good idea. Long time since you got your PhD.

Frank may have done it... but Frank also starts his charcoal with gasoline, drives a PWC at 80 mph, drives in Jersey, and jumps out of airplanes... not something recommended for everyone.

No, I actually did it, but I was observing the tank while doing so. A full 10" Hg of vacuum isn't actually required to move water from the head to the holding tank on my boat, so while watching the tank I was able to introduce a partial vacuum and release said vacuum before the tank distorted. These plastic tanks have a bit of flex anyway. You can see that as the sides flex convex when the tank is full vs. empty.

I don't use gasoline to start a bbq, but I do like the idea of using liquid oxygen. Having a natural gas fired grill at home makes this a moot point. My PWC only does 70 (indicated) but I'll probably change the impeller and grate this spring to get a few more mph out of her. There's got to be more speed from 255 horsepower. I drive in NYC, too. But Boston is the worse than either. Never jumped out of an airplane, but I did fly them for a while. My wife made me stop.

Just setting the record straight.

Why doesn't someone call Domitec/Sealand and see what there view is on plugging vents and putting a vacuum in the main holding tank... I'd love to hear their response...

They'll tell you not to do it. Why? Two reasons come to mind.

1. Someone who thinks "a little is good so a lot must be better" will implode his tank then blame Sealand saying, "You told me it would be OK!"
2. The Sealand tech on the phone doesn't have to stick his hands into the poopie pump. No stink on him for recommending not taking a short cut.

Best regards,
Frank

 

[Four Suns]

I think your point #1 is the issue. The bigger the tank, the harder it is to know when enough is enough... and the severity of the blockage, etc...