CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: Construction   Next in Forum: Compressive Strength and Fire Resistance Relationship
Close
Close
Close
25 comments
Member

Join Date: Nov 2015
Posts: 6

Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 2:29 AM

Hi Team, Good day.

My facility uses a vacuum toilet system made by EVAC which is tied to sewage holding tank and sewage treatment tank. The vacuum in the toilet is created in sewage holding tank. For some time now, we have been having issues of low vacuum in the holding tank thereby making it difficult for the toilets to be flushed. We have checked the vacuum pumps ok, educators ok as well. So what could be responsible for this low vacuum being generated in the holding tanks. I am expecting your feedbacks and solutions. Thanks.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26621
Good Answers: 699
#1

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 4:54 AM
  • Stop air leaking into the tank.
  • Lower the temperature.
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Member

Join Date: Nov 2015
Posts: 6
#3
In reply to #1

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 5:52 AM

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.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26621
Good Answers: 699
#13
In reply to #3

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 3:16 PM

<...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!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Aug 2005
Location: Hemel Hempstead, UK
Posts: 4102
Good Answers: 227
#2

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 5:03 AM

"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?

__________________
We are alone in the universe, or, we are not. Either way it's incredible... Adapted from R. Buckminster Fuller/Arthur C. Clarke
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3435
Good Answers: 87
#19
In reply to #2

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 9:37 AM

[ "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.
__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19898
Good Answers: 747
#4

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 6:24 AM

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.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Member

Join Date: Nov 2015
Posts: 6
#6
In reply to #4

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 7:07 AM

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

Register to Reply
Guru
Hobbies - Musician - Engineering Fields - Chemical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jan 2007
Location: Moses Lake, WA, USA, Thulcandra - The Silent Planet (C.S. Lewis)
Posts: 3891
Good Answers: 173
#8
In reply to #6

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 11:39 AM

Please stop calling it an educator.

Educator = teacher.

One little letter can change the whole meaning!

__________________
"Reason is not automatic. Those who deny it cannot be conquered by it. Do not count on them. Leave them alone." - Ayn Rand
Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19898
Good Answers: 747
#9
In reply to #8

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 1:35 PM

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.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Member

Join Date: Nov 2015
Posts: 6
#10
In reply to #8

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 1:38 PM

Thanks for the observation.

Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3435
Good Answers: 87
#20
In reply to #8

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 9:41 AM

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

Call them what they are: ASPIRATORS.

__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply Score 1 for Off Topic
Guru

Join Date: Oct 2008
Posts: 39624
Good Answers: 1570
#21
In reply to #20

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 11:44 AM

This is an aspirator.

This is an educator.

Two completely different animals.

Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member Fans of Old Computers - Commodore 64 - New Member Popular Science - Evolution - New Member United States - Member - New Member

Join Date: Oct 2013
Location: Illinois, 7 county region (The 'blue dot' that drags the rest of the 'red state' around during presidential elections.)
Posts: 3435
Good Answers: 87
#23
In reply to #21

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 11:58 AM

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.
__________________
( The opinions espressed in this post may not reflect the true opinions of the poster, and may not reflect commonly accepted versions of reality. ) (If you are wondering: yes, I DO hope to live to be as old as my jokes.)
Register to Reply
Guru

Join Date: Oct 2008
Posts: 39624
Good Answers: 1570
#24
In reply to #23

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 12:28 PM

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

Register to Reply
Member

Join Date: Nov 2015
Posts: 6
#11
In reply to #6

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 2:02 PM

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

Register to Reply
Participant

Join Date: Nov 2015
Posts: 1
#5

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 6:59 AM

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

Register to Reply
Guru
Hobbies - Fishing - Old Salt Hobbies - CNC - New Member United States - US - Statue of Liberty - New Member

Join Date: Mar 2007
Location: Rosedale, Maryland USA
Posts: 5203
Good Answers: 269
#7

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 10:58 AM

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.

__________________
Life is not a journey to the grave with the intention of arriving in a pretty, pristine body but rather to come sliding in sideways, all used up and exclaiming, "Wow, what a ride!"
Register to Reply
3
Guru

Join Date: Oct 2008
Posts: 39624
Good Answers: 1570
#12

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 2:47 PM

I have a most excellent solution.

Call a tech with the company who built/installed it and have then come on-site and SEE what the problem is.

It's hard for an anonymous forum to fix your unseen problem from half a world away.

Carry on now, there's a good lad.

Register to Reply Good Answer (Score 3)
Member

Join Date: Jun 2012
Location: liverpool england
Posts: 7
#16
In reply to #12

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 3:01 AM

can't fault you lyn, helpful as usual

Register to Reply
Guru

Join Date: Oct 2008
Posts: 39624
Good Answers: 1570
#22
In reply to #16

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 11:48 AM

Your track record is perfect.

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

Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19898
Good Answers: 747
#14

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 6:30 PM

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

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Guru
Engineering Fields - Retired Engineers / Mentors - New Member

Join Date: Dec 2006
Location: Brecksville, OH
Posts: 1568
Good Answers: 18
#15

Re: Low Vacuum Pressure in Sewage Holding Tank

11/12/2015 11:07 PM

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

__________________
"Consensus Science got us into this mess, then why can't it get us out?" : Rephrase of Will Rogers Comment
Register to Reply
Member

Join Date: Nov 2015
Posts: 6
#17

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 4:08 AM

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

Register to Reply
Guru
Australia - Member - New Member

Join Date: Feb 2008
Location: Australia
Posts: 1736
Good Answers: 201
#18

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 5:34 AM

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.

__________________
Just an Engineer from the land down under.
Register to Reply
Guru

Join Date: Nov 2007
Location: Eastern Arizona mountains on Route 666 about a mile from God's country
Posts: 1677
Good Answers: 121
#25

Re: Low Vacuum Pressure in Sewage Holding Tank

11/13/2015 7:39 PM

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.

__________________
They said; "Brain size?" I heard; "Train size?" so I said: "I'll take a small one, thank you."
Register to Reply
Register to Reply 25 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

adreasler (3); agua_doc (1); gissy (1); Just an Engineer (1); Kalu (5); lyn (4); Mikerho (1); ozzb (1); PWSlack (2); Randall (1); SHOCKHISCAN (1); Tornado (3); woodennichols (1)

Previous in Forum: Construction   Next in Forum: Compressive Strength and Fire Resistance Relationship

Advertisement