Direction of flow through valves

[zkzaza]

Dear all,
Please help a beginer!!!!
My question is:
Are there types of valves that are stricly directional or stricly unidirectional? Or is it that every type of valve can be both depending on the specific design? i.e. are all butterfly valves directional? are all ball valves uni-directional?

Thank you in advance!

 

[zdas04]

In general terms,
[ul]
[li]valves labeled "block valve" (e.g., floating ball, trunnion ball, gate, plug, or butterfly) are bi-directional[/li]
[li]valves intended for control can either be strictly uni-directional (e.g., Fisher V-Ball, pressure regulators, back pressure valves) are strongly uni-directional. Some control valves (e.g. manual globe valves) have a preferred direction but reversing the flow is not a huge issue.[/li]
[li]Check valves are uni-directional.[/li]
[/ul]

Some people sell butterfly valves for control. I've used a few and have never been at all happy with their linearity (i.e., a 5% increase in valve position will give you 10-30% more flow in the first 20% of travel and <1% more flow in the last 50% of travel). Even the fancy double (and triple) eccentric valves have crappy linearity. I only use them when I take over a project that already has them and I can't talk them into throwing them away.



David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat

 

[wafer71]

Before one can answer this question, you must look at the trim and sealing surfaces. On some ball valves, the seats are designed to have the process apply pressure on the ball when closed which in turn applies pressure on the seal to aid in sealing the valve closed. Best is to always look at the valve body. Manufacturers have placed this arrow on the valve body for a reason. If someone elects to install a valve in the opposite flow direction as indicated on the valve body, then that individual is taking on considerable risk should a leak or worse yet a failure occur as a result. My recommendation always follow the manufacturers flow indication on the valve body. If no arrow consult with vendor to verify, and do so by means of email should anyone question you in the future.

 

[nobog]

A heart valve is one-direction, but that's not probably not what you are looking for .

JK