Modulating types Butterfly Valves 4

[Kandeel76]

hi All,

I need valve professionals to reply my below question.
In sand filters and backwash applications, MODULATING electro-pneumatic butterfly valves is preferred to use for filing, rinsing and backwash, why they do not use ON-OFF butterfly types?

Why MODULATING??

The below web link for reference.

http://www.festo.com/rep/cs_cz/assets/pdf/Rieger_IA_Valves_EN.pdf

Thanks in advance

Kandeloo

 

[stanier]

When backwashing you want the flow rate to be constant. As the level in the filter rises the head, hence the flow, on the pump changes . Hence the butterfly valve is used to control flow rate. Ergo it has to modulate to provide a constant back pressure. backwash pumps tend to have low heads and hence small changes in head change the flow rate markedly.

In addition to this you may consider a water and a water and air wash. They have different flow rates.

This is not a question for valve suppliers but for water treatment engineers. Your OP would be better in the Water Treatment & Distribution forum.

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

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

 

[gerhardl]

Agree with stanier (good post). Another thing is the modulator type discussion (electro pneumatical) compared to electric, and the parameters of operating a modular butterfly valve without getting cavitation (low pressure differences, slow flow).

But if we start this discussion, we are starting getting far out on a side-branch.

(Pneumatic contra electric operators both have some 'religious' fanatics.)

 

[stanier]

The other thing to remeber is that butterfly valves may be cheap but they dont make the best flow control valves. invariably one has to reduce the size by several line sizes to get adequate control. In this application I have use two buttefly valves in parallel to meet the varied conditions.

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

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