Valve Stroking Speed

[tsenthil]

Can anyone help how to determine the Solenoid/Air Filetr Regulator Cv required for attaining stroking speed in a Rotary Valve

I have details like this

Actuator Volumetic displacement - 165 litres
Ball Valve closing time reqd - 15 Secs
Ball Valve Opening time reqd - 15 Secs

is there any caluclation available to calculate the Cv required to attain this stroking time?

Advance thanks for the help.

 

[gerhardl]

Practical advice:

Solenoid valves will for any certain nominal diameter vary greatly (depending on type and brand) in real Cv. Cv or air capacity might be given on different basis.

1. Check actual nominal light opening of the solenoid valve.
Exsample: a 1/4" valve can be anything from less than one mm nominal opening up to 6mm.

2. Check the basis (nomenclature) for the given capacity for the solenoid valve.

3. Any qualified (good)solenoid supplier will give you directly the answer to your question. You have to make some assumptions though.

4. It is always wise to go up in bore on the solenoid to have enough capacity, and then throttle with throttle valves to reduce actuator speed. Remember that not only solenoid valves but also pipelines, inlet to actuator and internal actuator borings (if any) will influence speed, also sufficient air pressure and air amount available.

5. A nominal bore 1/4" with 6mm throughlet and Kv about 1,2 (Cv = kv times 1,2 = 1,44) might be sufficient, based on an assumption of 167 l/15 seconds times 3600 seconds -> 40Nm3/hour (Qn) necessary. You also have to assume the pressure difference. For supercritical: Qn=13,36 x P1 x kv for subcritical: Qn = 26,7 x kv x (root of deltaP times p2).

P1 being supply pressure, P2 pressure inside actuator to get sufficient amount in at a pressure to move the avtuator.

As the actual mecanical performance and necessary torque is unknown, I would be much more comfortable selecting a 1/2" with nominal bore 12mm, kv=3,0 (Cv =3,6), and throttle down to suitable speed for the actuator.

 

[JimCasey]

Find your local Automax distributor and ask for a copy of Autosize 3.1. It has a routine for calculating stroke times with known displacement and Cv of accessories. Also it works backward and will give you a required Cv if the volume and stroke time are specified.

Automax is a Flowserve product. Look in flowserve.com, in the sales locator, and you can contact your local Automax distributor.

 

[tsenthil]

Dear Gerhard/Jim

I came across the enclosed calculation for calculating Stroking speed for linear valves.. will we use this for Rotary valves?

 

[gerhardl]

No, you would have to define x (the travel) for your rotary actuator.

Geometrically this could perhaps be approximated as the distance along the circle the 'midpoint' of the volume within the actuator travels to complete the turn. Midpoint then defined as the point where half the total volume is further out on the circle and the other half is further in. (Eg. NOT half the distance along the side wall as radius endpoint)

I cannot comment on the quality of the formula in either case, other than that presumptions must be backed by actual experience.

If critical to obtain not more than 15 seconds, I would still have used 1/2 inch and throtteled.