Pump Control Valve for Sewage 1

[broomerh]

Hello,

I require a pump control valve for a large pumping station, pumping unscreened sewage.

The valve would be normally used for controlled pump start-up and shut-down against the closed valve, opening/closing at a controlled rate to prevent excess pressure surge.
Very occasional throttling performance would be required while repriming the system.

Could you tell me the advantages / disadvantages of Eccentric Plug Valves or Ball Valves for this purpose.

The main pipe dia is 1400mm (56") for a flow of 5.0m³/s (79,000gpm). I was assuming a valve of ~ 1000dia (42")

regards

 

[stanier]

I have used Dezurik eccentric plug valves or RED pinch valves for such services.

You could consider a pair of knife gate valves in parallel. One opening first then a second to give full flow.

I suggest that a VFD driven pump may be rpeferable as stringy particles can clog valves.

Have you carried out a waterhammer analysis to determine if you need such a valve at all?

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[gerhardl]

Agree with stanier, and in addition some points:

1. Flow analyis in addition to determine necessary size. First meters from pump and valve size could perhaps be somewhat smaller than main pipe. Note: I get about 6,4 m/s from 1000mm valve and 5000l/s. Something wrong? Seems very high in my experience!? Check the best economical solutions for size pump and valve in combination.

2. In stead of two valves also a station split up in two or several parallell pumps and valves for the first meters. Higher price but advantages for maintanence and possible process if lower volume at times. Flow into main to be regulated/controlled from each, and pipes to be constructed to even out supply from the parallell pumps. (One pump could dominate the pressure and hinder a pump downstream to operate properly, checkvalves necessary)

3. Valves: both a question of price and maintenance.

a) Ball valve. Should then be double eccentric (for instance type Erhard). References from Berlin, Germany. High price, Long troublefree lifetime.

b)Eccentric plug valve: comparable to ball valve.

c) Knife- gate valves. In Scandinavia knife-gate valves of good construction without pockets would probably be preferred. Valves exists where a restrickting (regulating) plate with triangular (to regulate small streams) or pentagonial (to regulate larger streams) may be integrated in the valvehouse, direct in parallell with the knife. Usual masss-produced standard up to 600mmm with restrictions on working pressure. Also available from a number of companies as special items with higher diameters. Electrical, pneumatical or oil hydraulic constructions for actuators normal. Will require regular service. Change of valve sealings each 3rd to 10th year (factory to give info). 'Oiling' if wastewater doesn't contribute or actuator requier this. (Eccentric plug-valve better on technical aspects)

d) No personal experience for pinch valves this size. Would recommend focus of manufacturor that can show to long standing time for equal size and purposes with exact references to detailed construction/materials. Price? Maintenance?

 

[broomerh]

Thanks for the replies.

Re: Stanier's point of 'do we need pump control valves?'
We have a deep shaft pump station with high flows & high heads (we have a total of 10 pumps - each at 5m³/s).
PCV's (and generally ball valves) seem to be a common solution on similar installations, however on considering it, a standard swing NRV with small dia bypass (to mitigate the surge/water hammer effect) would seem to work.
Have you seen any examples of high flow, high head, sewage systems using swing check valves?


Could you tell me a vendor for the knife gate valves with control insert.
I think we may have difficulty with safe closure rates if we tried to use KGV's...


NB. The large majority of the total head is static head - so limiting the usefulness of the VFD when it comes to start-up and shut-down.

 

[gerhardl]

Please clarif, giving pressure (head) and pipeline diameter. Single lines or feeding larger common? Comments?

 

[stanier]

I would not rely upon a swing check valve. ARD Thorley describes these as "agricultural at best" when considering transient analysis. Refer Fluid Transients in Pipeline Systems".

In this reference a solution is shown for the type of installation you describe. A controlled opening air valve is located at the top of the riser before a non slam check valve. The discharge of air limits the velocity in the riser and prevents a high transient pressure when the column of liquid hits the closed check valve.

Alternatively you might consider a gas accumulator at the surface. These have been used in sewage service. Check out Olear (Charlotte) website.

You might consider the Surgebuster rubber flap type or Red duckbill check valve at the surface if the pressures permit. These are commonly used in sewage service in Australia.
Performance of check valves in dynamic situations are describe in the above reference and Pressure transients in Water Engineering by Ellis. the latter has a good section on Red duckbill valves.

Have you done a surge analysis yet?

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[gerhardl]

In addition to staniers references and solution to prevent waterhammer:

In my experiences a checkvalve of 'non-slam' construction near pump outlet (some meters away?) will also prevent gulping and slams when low flow and prevent waterhammer if abrupt cllosure. My experience is from far smaller systems with low flow. Non- slam valves of construction type top-hinged disc/flap, full opening (by large valvehouse) checkvalves with outside spring. Optionally with bypass and/or connection for flushing. I do not know if the construction exists in suitable size for you.

 

[stanier]

Another problem with swing check valves is sewage service is the hairs. string and condoms that wrap themselves around the spindle and bind the disc. Eventually the reverse velocity is so high the disc slams closedand damage occurs. I have seen pump stations where the operators refuse to enter because the noise is frightening.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/

 

[broomerh]

Some more details:
Each pump duty point is 5.0m³/s at 90m.
Each pump has a 1400mm dia vertical riser combining at ground level into an expanding manifold (2.8m dia at widest point).
The pressure in the manifold is very low (~2-3m above sofit)

We are in the process of doing a surge analysis at the moment.
The initial surge recommendation was a duckbill or surgebuster type valve just below the high level manifold with vacuum breakers and air release valves.
But if a solution was possible at pump level with soft closing check valves (like the surgebuster valve) and a bypass (similar to the sort of bypass around a NRV often used on the outlet to surge vessels) this would be much simpler.

 

[stanier]

I suggest you dont jump to a solution before you have done the analysis and have the numbers. No point n having a convenient solution if it doesnt work.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King

http://waterhammer.hopout.com.au/