Estimating static head on existing system 6

[Jimmyvanskip]

Im investigating the feasibility of installing VSDs on a system and am aware that potential savings are impeded on a system with a relatively high static head.

My question is: How do I determine what proportion of total head on an existing system is static head and what proportion is friction head? There are no pipe isometric drawings/ P&IDs or system curves available for the system. Further more I can't "walk the line" and develop the system curve again from scratch as most of the pipe runs are inaccessible.

All suggestions most welcome.

 

[TD2K]

If you are going from a pump through a control valve and then through your associated equipment and piping to the destination you should be able to estimate the power savings by measuring the pressure drop the control valve is taking. Depending how the operating conditions change over time, you may need to get several measurements to accurately estimate the total power savings over a year.

 

[BigInch]

Turn the pump off and gauge the pressure at its discharge just after it stops. May not be totally accurate, but it's probably close.

Don't forget that it may not always be just simple static head that's a problem. Any relatively high head that must be maintained more or less at all flows, such as the pressure necessary to pump into a boiler, or downstream pipeline holding a nearly constant pressure, will result in the same poor performance when coupled with a vsd.

What would you be doing, if you knew that you could not fail?

 

[bimr]

As BigInch stated, the static head is that pressure that exists when the system is at rest. Turn the pump off and measure the gauge pressure at the pump.

You will also need to add to the static head any constant pressure from items such as pressure regulating valves, or any backpressure that you are pumping against.

 

[rmw]

Dont forget components that are variable pressure loss in your system like strainers or filters that can clog up. If you measure your system as recommended above with a clean strainers/filters, etc, system head loss can change as it/they collect 'stuff'.

rmw

 

[rutherford703]

It is easy to find the static head. You don't need P&ID and ISOs of the piping. The only information needing to know is the elevations of your pump and the exit of the piping. The elevation difference is the static head of the system.

When people install VSD, normally it is required by process such as to control the flowrate of the pump or control the level of the vessels.

VFD (variable frequency driver) is better than VSD (variable speed driver). Some people use them interchangeably.

 

[stanier]

rutherford703

Static head is the difference between the level of tank up stream and tank downstream. It is not the pump level. There are quite a few pumps many metres below the tank level and act as booster pumps between reservoirs.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

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

 

[bimr]

rutherford703

A variable-frequency drive (VFD) is a system for controlling the speed of a rotational or linear alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. VFD's are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, microdrives or inverter drives.

 

[stanier]

But there are many other drives that could be called VSDs and not all have anything to do with electrical power.

"Sharing knowledge is the way to immortality"
His Holiness the Dalai Lama.

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

 

[BigInch]

Diesel engines, for example.

What would you be doing, if you knew that you could not fail?

 

[rutherford703]

Stanier,

That's what I mean. You can easily find the static head for the pump from the suction tank level and discharge tank level or the discharge point.

 

[bimr]

rutherford703

Yes, the poster is interested in determining the static head. But it would be a mistake to tell him just that and neglect the other constant pressures in his piping system.

If your system consists of constant pressure losses, then the potential for energy savings with a VFD will not exist.

For example, if you have a system with zero static head, zero friction head and are pumping into a pressurized tank, there are no energy savings if you switch to a VFD control.

 

[BigInch]

yes the point is becoming diluted.

What would you be doing, if you knew that you could not fail?