8 replies to this topic

[icingrock]

I have new process requirement for new pumps.
One of the existing can fulfill all the requirement except that the TDH is much larger than needed.

Of course, there is control valve on the discharge pipe of the pump. The discharge goes to a distillation column as a reflux.

Do I have to worry about the excessive head or it can be covered by the control valve sizing (Cv) ?

Please comments.

P.S. I really want to get synergy in spare pumps with less pump models. That's why I don't to want to buy a new model which probably fits the new application better.

[latexman]

To save energy:

Idea 1 - use a VFD on the pump to control flow.

Idea 2 - use a 2 speed motor on the pump and provide less excess head to the CV.

[Rahimzadeh]

Dear:
:At first you must clear us about your type of pump
in centrifugal pump if your pump equipped with circulation line you can open it and change pump working point , with increasing flow the pump TDH will be reduced.

[S.AHMAD]

1. There is no operational problem since control valve will absorbs the extra energy.
2. Another alternative: consider reducing the impeller size if economically justified. This is normally the cheaper option. With current high energy cost, it can easily justified. Otherwise, just pay for the wasted energy.

Edited by S.AHMAD, 27 March 2012 - 07:43 PM.

[Dacs]

Out of curiosity, would letting the control valve takes in the increased head affect its control?

I suppose having a higher pressure drop will reduce the % opening of the valve and may have to work on a smaller range to control the process.

On topic, would a Restriction Orifice do the job of handling the extra head of the pump?

[S.AHMAD]

Dacs
1. Yes! I agree with you that if the valve opening is too low, the valve control-ability is affected.
2. Under this situation, the most common approach, without any additional investment cost, is to pinch down the block valves e.g. at pump discharge, Control valve inlet & outlet.
3. Orifice plat will also the job if pinching of valve is not viable.

[fallah]

Regarding the OP statement that the TDH is much larger than needed (not specified how much) the discharge line should be checked if can handle the new pump discharge pressure, because it might the new pump discharge pressure be even higher than old pump's shut off pressure!

Edited by fallah, 29 March 2012 - 01:48 AM.

[S.AHMAD]

Agree with Fallah. Need to check also the flange class.

[Dacs]

And since we're going on the specifics of the pump, might as well check if the pumped fluid is compatible with the intended service of the replacement pump (such as appropriate seals).