Adding Headloss To Piping System?

[jobarr]

Hello all,

Is there a reliable and predictable way to add headloss to a pipe system so that I can stay on a pump curve?

If there is little to no elevation head, then the TDH relies entirely on headloss in the pipes. In order to generate enough headloss in the pipes to develop a TDH that works for many pumps, I have to increase the pumping rate significantly. Unfortunately, I then end up with a pipe velocity greater than 5 ft/sec which appears to be a recommended limit.

For example, one of my projects requires me to pump stormwater a distance of 600ft at around 350gpm. There is only about 5ft of static head that the pump must overcome to pump the fluids out of the sump (ground surface is essentially flat). If I use a 4in PVC pipe, I can generate enough headloss in the 600ft of pipe to put me on the pump curve (Flyght 2640). However, the pipe velocity is around 9ft/sec. If I try to reduce the pipe velocity by going with a larger pipe (6in PVC), hardly any headloss is generated in the pipe and I am hardly on the pump curve.

Are there any common/reliable ways to add headloss to the system? I would prefer to avoid using a manually adjusted throttling valve because I don't want someone to open it all the way without understanding why it is there.

I would appreciate any comments. Thanks.

 

[LittleInch]

First off,

The velocity figures you've listed are ROT or figures which are much more valid as guidelines for economic velocities for long pipelines.

If, for some reason, you can't match your pump duty to your service requirement which is the best way, then 9 ft/sec is ok. There are no real velocity limits unless you've got a lot of particulates when erosion can become an issue.

If you have a fixed head / flow curve then the only other way to do this is introduce a restriction orifice to create additional head loss as flow increases.

The design options available to you will create the most economic way to do this, either a certain pump and a smaller pipe, but more operating costs or a bigger pipe, but a smaller pump.



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

 

[bimr]

You need to start over with the correct type of pump. Submersible pumps are probably not a good selection for this application. Ask your pump supplier to select a low head/high flow pump for a storm water application.

 

[Artisi]

There is no reason or problem to operate at higher velocity in your situation as it's a sump pump and will be used occasionally.
Probably not the best pump for the application.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[georgeverghese]

Try a smaller line size that will generate more headloss to get you back to some where close to BEP on the pump curve, if that brings you close enough to 350gpm.

 

[Valvecrazy]

With a pressure sustain valve you can adjust how much head or pressure you want the pump to see. We use pressure sustain feature on lots of irrigation type pumps. Sometimes the same pump used for irrigation at 50 PSI will be used to fill a pond or something and the pump runs without any head against it. This usually causes the motor to run in an overload condition. So we install a pressure sustain valve and the pump always sees 50 PSI, even when a valve is completely open to fill a pond.

 

[Artisi]

Come on now guys/gals, this is a stormwater sump pump, not a nuclear power plant pump. Buy a pump that is capable of somewhere near the (guessed) flowrate, put it onto some 4"pvc pipe with a float switch for high/low level, throw it in the sump and forget about it. It can be one of the many many thousand thru out the world doing this same job day in and day out.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Valvecrazy]

As long as it is not overloading the motor I would let it pump.