Low Vacuum Pressure in Sewage Holding Tank

• Stop air leaking into the tank.
• Lower the temperature.

I have checked there is no noticeable air loss from the tank. Then, I can't think of how to lower or reduce the system temperature as it works on ambient but if you have idea on how to reduce it, please you are highly welcome.

<...no noticeable air loss from the tank...>

Stop the air leaking INTO the tank. Please use Steam Tables to relate the temperature in the tank to the maximum vacuum that can be created in the tank. Please re-post with the maximum vacuum that is being created alongside this number. The difference between these represents the air leak!

"educators" ?

I'm guessing that the pressure sensors in the holding tanks are programmed to turn on the vacuum pumps when the pressure gets up to a certain level, and, off again when the pressure gets down to a certain level.

Do you have an independent way of checking the pressures at which the pumps turn on and off?

[ "educators" ? ]

Spell-check has failed him, I believe he meant EDUCTORS, also known as 'aspirators.'

Similar to air-entrainment nozzles, these use moving air to pull something into the stream. with air entrainment, the small air jet drags along the 'static' air next to the nozzle to increase total CFM⁽¹⁾, for aspirators, the moving air⁽²⁾ pulls liquid from an opening in the side of the aspirator into the stream.

Now that I'm thinking of the similarities between air entrainment and aspiration, I'm wondering if those vacuum systems that use compressed air for energy use a similar system; the moving air 'entraining' the air in the 'vacuum chamber' and drawing it out, thus dropping pressure in the vacuum line.

Notes:

1. Since you're getting 'free' CFM, I'm assuming there is an unspoken 'cost' for this 'free energy,' and I'm guessing it is taken from the heat energy in the air, cooling the local area by a fraction of a degree.
2. It does not need to be air, any fluid will work. I know of eductors from the cleaning/sanitizing chemical dispensers we use in the plant, those use eductors to mix the concentrated chemical with the clean tap water to get the correct strength to to the job.
   

Maybe an eductor is clogged (or its injection nozzle worn) so that it is less effective. Or whatever source supplying water to an injector pump may be blocked.

I have removed educator valves for cleaning and even changed out the flappers on them. Water sources are also ok.

Please stop calling it an educator.

Educator = teacher.

One little letter can change the whole meaning!

I think he's being bitten by some dumb spell-checker. In my post, I had to edit out an "a" that I didn't put there.

Thanks for the observation.

Yeah, who decided to call them 'eductors' anyway?

Call them what they are: ASPIRATORS.

This is an aspirator.

This is an educator.

Two completely different animals.

Okay, I get it, one is intended as a pump, one is intended as a mixer.

Although, if we're going into technical details here, this is an EDUCTOR:

and this is an EDUCATOR:

We've got to keep an eye on what the spelling check⁽¹⁾ routines tell us. Don't let the computer do your THINKING for you, leave it to do the lookups and number crunching, and double check its results.

Notes:

1. Not 'spell check' there are no spells being checked, unless you're writing a book on magic, or quoting the three witches from The Scottish Play⁽²⁾.
2. I grew up in the Theatre, I will not speak the Name of that cursed production lightly.
   

Damn! We used eductors by the edozens in one of my former lives.

You are dead right man. Facing great pressures on the installation as the entire toilet system have collapsed. My apologies.

Its a holding tank. Varying volume in and out. Stronger vacuums when tank is near capacity. Think of a vactor truck its a strong vacuum at first but has to completely loose its vacuum every time its emptied then has to build all the way back up.

first but slowly

How do you know the vacuum is low at the holding tank. Or the vacuum pump is working right. Does the manufacture have vacuum specs on the pump and do your test of vacuum match or come close. When you close the valve to the toilets does the the tank hold the rated vacuum.

can't fault you lyn, helpful as usual

Your track record is perfect.

You've never made a useful, constructive comment since you came here to troll the forum.

Find the toilet with the stuck tampon, rag, or whatever in it; remove the obstacle.

Do you have any time-frame for when the problem occurred or when things started to go awry?

Alright gents, thanks for all your contributions. I appreciate.

Some good hints already in previous posts.

One toilet in system with an obstruction allowing leakage (of air) is possible.

Another is a change in the relative height of the pans being serviced by the system to the TWL in the chamber.

Another might be obstructions in the lines (close to the pans) that is restricting flow. [Your pressures would show as OK, but just not clear the pans.]

You may have hydraulic "jump" in the system if any pipe subsidence has happened. Each air lock created robs the system head from the serviced pans unless the system is specifically designed for that situation.

Another might be pipe joint leak.

finally, could be return leak from treatment tank through eductors/pump mechanism.

Is problem "system wide" or just isolated to specific pans (longest pipe run from tank.)?

Is problem "new" and had sudden onset, or has developed over time?

Have there been additional pans added to the system since original install?

Are you able to isolate sections of the system for investigation?

Have all pan seals and other service components been serviced and checkked regularly?

Where I work operates a vacuum sewer system for over 300 properties. A little different from what you have, but some common symptoms.

Isolate the tank from the rest of the system and see if it the low vacuum is still present.

If the vacuum pressure is normal then there is a leak outside of the tank in the conveying system.

If the vacuum pressure is not normal; there is either a leak in the tank valves, or associated instrument ports, or the flow path between the tank and the pumps and eductors is restricted.