ARV/PRV/VB Best Practices

[NW_Wash_Eng]

Hello all!

I am working on refining and improving a piping system for a facility that is in design. One item I would like to reduce the overall use of (if possible) is air relief valves we have. Currently, we have been cautious and included an air relief valve at every local high spot and one air/vacuum relief combo valve at the absolute high point. The pipes in question are all on a pipe rack that was designed with 3 to 4 levels, each 36" apart. Some of the small pipes (1", 2", 3") have quite a few undulations to fit around the larger pipes (4" through 12") due to lack of space available on each level. In other words, some were fit where they could and squeezed through where they needed to go. My first step is leveling out the pipes as much as we can, but in some places that is just not going to work.
I assume the "proper" answer is yes, I need air relief valves at every location a pipe drops in elevation. But in actual practice how much does air build up actually affect the system? I assume it has to do with reducing pump performance. Is there a correlation between pipe diameter, flowrate, and how much of an elevation change the pump can "push" the air through? Or is there any guidelines/best practices for such an application that I should be following?
My follow up question is about some literature. I would quite like to dive a little deeper into piping system design as a whole, as I am quite new to it but have very much enjoyed it. Any recommendations? I have been looking at "Piping Systems Manual" by Brian Silowash, but haven't pulled the trigger yet.
Thanks!

 

[LittleInch]

The usual velocity to use which sweeps gas out of pipes with liquid is 1 m/sec.

This works even when pushing gas bubbles vertically down.

If you have gravity lines or syphonic systems then air is not good, but if these lines are all forced flow by pumps or pressure then you probably don't need as many valves.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

What kind of facility is this that it needs air and vacuum valves everywhere?
Normally most facility piping is designed to operate with closed piping systems, so these valves are not required anywhere.
Why do you think you need so many?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

You sometimes find vent points used during testing or commissioning which are just screwed plugs and not valves etc which are vulnerable to damage and corrosion. But if in filling and testing you can flush the pipe with enough velocity then you really don't need so many. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[NW_Wash_Eng]

@ LittleInch
When is the 1m/s rule of thumb NOT applicable? I'd also be curious to know where that number came from. Either way, thanks for the input!
As far as gravity fed lines, they almost always stay below the outlet of our tanks for this very reason. We also hardly ever have gravity feed only areas.
I find it curious you bring up the venting during commissioning stage. We toyed with this idea, but a majority of our high points are either not easily accessible or a few hundred feet from the building. Doing this once on start up would be no issue, but we have some lines that routinely need to be replaced.
@1503-44
We consider ourselves waste water treatment, but this facility specializes in digested cow manure. ARV's were a last minute "panic" addition as someone brought up air lock. Due to scheduling, it was deemed better to over buy and remove at a later date if we could.
Most of our lines are from skids or tanks, as you'd probably expect. Since most of these tanks are vented to atmosphere, or even open top, does that mean we are not operating in a closed loop system? Or are you referring to the piping itself being a closed system? I believe I am getting caught up in the nomenclature here, so my appologies for the novice questions!

 

[1503-44]

Generally your pipe pump system should be designed or operated such that you do not get vapor locks.

What's the story about replacing your pipes on a routine basis. You must be treating some very nasty stuff.

Bubble flow velocities.
Interesting charts of terminal bubble velocities in a watery solution.
I just knew somebody was going to ask that question one day.

They pretty much limit out at 1 m/s, which should usually be your minimum pipeline fluid velocity anyway. 1 m/s minimum to 3m/s maximum.

And a slide presentation of where I found the last chart attached.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[1503-44]

Attached here

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

Depend son the angle of the pipe and the direction of flow of the bubbles.

So a flat pipe or one going only say 45 degrees down doesn't need so much flow.

There have been a lot of papers and experiments and it might be a bit more than 1m/sec, but its in the right ball park.

see attached and on the next post


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

next one

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[NW_Wash_Eng]

@1503-44
Struvite build up requires us to replace the piping every so often. We are hoping to get a year out of it, but 6 months is when we start to notice the pumps ramping up to maintain flow rates.

@LittleInch & @1503-44
I very much appreciate the files and graphs! I will be taking a look through these this afternoon and seeing if I can start to understand this further. Thank you so much!

 

[1503-44]

Struvite remediation

https://m.youtube.com/watch?v=VKX7EPHKulw

https://m.youtube.com/watch?v=B8d0HOHWTCs&pp=QAFIAQ==

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[NW_Wash_Eng]

We are no stranger to struvite formation/cleaning/prevention. Replacing our pipe instead of cleaning (which by the way, is not much pipe) was an uptime based decision. Cutting out the PVC and installing new has been historically quicker for us to get our system back operational. Admittedly, that is where my understanding of the knowledge of the chosen direction stops. I can state, however, that we are working on developing a cleaning cart that we can use as a temporary recirculation loop to clean pipes, valves, etc. Until then we are breaking out the Sawzalls.

 

[1503-44]

That's OK. I learned something.
Good luck with the cleaning system.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[NW_Wash_Eng]

Thanks, 1503-44, it has been a lot of non standard practices for me (a relatively new employee to this company) to get used to.
And thank you to all who responded. I believe I have enough information and data to back it up to move forward with significantly less ARVs in our system.