Surge Tanks vs. Pump Control Valves

[civilwtrengr]

I am considering installation of either a surge tank or pump control valves to solve a surge problem associated with starting/stopping of 60Hp, 550 gpm pumps. This lift station is pumping treated wastewater effluent. The cost for both options is about the same.

Here's my question:

Can a surge tank provide the same level of surge reduction as a pump control valve? This is an important application, as the forcemain has broken several times in the past year due to normal operation of the pumps. The existing forcemain is fatigued, so we're looking to reduce the surge pressure as much as possible.


Any input/thoughts would be appreciated.

 

[SNORGY]

At 60 HP, I am wondering if it might be almost as cost effective for you to (if the motors are not already inverter-duty rated) to look at new motors (that *are* inverter duty rated) and VFDs, or at least "soft start" options.

Regards,

SNORGY.

 

[civilwtrengr]

Thanks for the input. We have been considering adding VFDs and soft starts, however due to the existing site constraints and existing MCC, VFDs are much more expensive.

Soft starts may be an option (about the same cost as a surge control tank) however, I'm concerned a soft start will only ramp up/down flow from 1 - 20 seconds. At a closure time of 20 seconds, I am calculating a surge of about 38 psi.

Any additonal thoughts/input would be appreciated.

 

[SNORGY]

It's true...if the E&I&C infrastructure isn't already in place at the site, VFDs lose in the economics analysis. Given the choice between the control valve and the surge tank, then, I am inclined to try a slow-stroking control valve. But the tank should kill the surges for sure.

Regards,

SNORGY.

 

[cvg]

surge tank is arguably more effective and relatively fool proof compared to any sort of electro-mechanical control system.

 

[BigInch]

If the problem is the forcemain, then turn down the operating pressure and lower the velocity. That's the solution you should be looking at.

You speak of a control valve. Would that be a downstream pressure control valve, or one of those "bypass surge relief valves"?

If you want to look elsewhere, you could try a "bypass surge relief valve", as opposed to a common surge valve, which would be located on a T-off from the main line and typically routed to a surge tank.

VFDs won't work when the pump goes down on power loss.

If you have two options that cost equally, pick
1) the simplest technological solution or,
2) the next simplest technology with the smallest footprint.
3) if the simplest tech solution has the biggest footprint, I'm not going to argue with whichever one you pick.


**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[civilwtrengr]

I appreciate all of the input. Unfortunately, the flow and the head are set, we cannot adjust them. The pump control valves we are considering are slow open/close valves, just downstream of the pump. The pumps actually start against a closed valve that opens/closes slowly to prevent surge.


Can anyone recommend some surge tank manufacturers?

So far, I have been able to only find one manufacturer of bladder-type surge vessels. And, cost for this one manufacturer are about $50/gallon.

Thanks a bunch.

 

[BigInch]

Right, those valves should work fine, provided there is still something left in the pipe.

What vessel size do you need? Have you made a simulation to find out what volume you need to relieve to keep pressures lower than allowables?



**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[civilwtrengr]

A simulation was performed, and it appears an 800 gallon tank will provide the adequate pressure reduction.

 

[BigInch]

Another option would be a typical surge valve on a T-off, routed back to the pump intake reservoir, provided you have a reservoir nearby that will hold an additional 800 gal. If you don't have a reservoir, 15 feet of 36" pipe and some end caps will hold 800 gal. Maybe a 20 ft section, in round numbers ... so to speak.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[stanier]

A surge tank is far more reliable, needs less maintenance and would probably cost effective comapred to a valve solution.

 

[BigInch]

Yes. If the 20 foot pipe section is made suitable for full pressure, it could be used like that; without a surge valve in the line routed to it, with about 25% air content in the tank when at pump discharge pressure.

**********************
"The problem isn't finding the solution, its trying to get to the real question." BigInch

http://virtualpipeline.spaces.live.com/