Choice of Valves: Gate vs. Ball
Choice of Valves: Gate vs. Ball
(OP)
I'm doing some research into the choice of valves for subsea service. What are the advantages and disadvantages of using ball valves instead of gate valves?
Some details of the intended service:
• high design pressure: >70 MPa (>10.2 ksi)
• bore sizes: 13 to 18cm (5" to 7")
• valves will have a geared operator, and be operated by ROV
• water depth is >1000m (>3,281 feet)
• the frequency of operation will be only a few times during the design life (~25 years).
• valve should be open for all of life, but could be closed at some point
• operational fluids will be raw, directly from a subsea well
many thanks,
TJAvery
Some details of the intended service:
• high design pressure: >70 MPa (>10.2 ksi)
• bore sizes: 13 to 18cm (5" to 7")
• valves will have a geared operator, and be operated by ROV
• water depth is >1000m (>3,281 feet)
• the frequency of operation will be only a few times during the design life (~25 years).
• valve should be open for all of life, but could be closed at some point
• operational fluids will be raw, directly from a subsea well
many thanks,
TJAvery





RE: Choice of Valves: Gate vs. Ball
RE: Choice of Valves: Gate vs. Ball
I will echo, 11echo's post, but add that operating one, two or "a few" times in twentyfive years warrants some consideraton to crustation growth and corrosion. This has been done before, the requirements are not new! Search subsea valve sites, etc. Call and discuss your needs with various manufactures. Check with experienced fellow engineers within your company.
The last thing you want to have happen in a really critical situation is THAT valve's failure to close when you really need it to.
Good Luck
pennpoint
RE: Choice of Valves: Gate vs. Ball
a) even with a 1/4 turn valve I would be very careful when closing a long piping system, if you do this too fast with flow you could have transient pressure peaks (geared actuator is a good thing).
b) I suppose the fluid may have solids and this could prevent a good closing of a Gate valve and with long periods between action I would feel better with a ball valve. Still, I would follow the advice of pennpoint.
RGS
RE: Choice of Valves: Gate vs. Ball
Please check with The Valve Doctors, CCI. (Tel:1-949-858-1877)
RE: Choice of Valves: Gate vs. Ball
is it critical that the valve closes when it should close?
and:
would a valve test (close and reopen) disrupt the service?
if the answer to any of the two questions is YES... then i would consider having two valves in parallel so you can test them periodically and make sure they will operate when required.
By all means the ball valves will have better tightness than the gate valves and will not be subject to the same wear and tear because the erosion will not affect as badly the sealing surfaces.
HTH
saludos.
a.
RE: Choice of Valves: Gate vs. Ball
The ball valve can be re-opened if there exists a large pressure drop across across the valve , but a closed gate valve cannot be easily opened if a large DP exists.
RE: Choice of Valves: Gate vs. Ball
1. 5" to 7" bore pipe? Aren't those rather obscure line sizes?
2. Even if you went with a ball valve, you're correct you'd still need a geared operator with a 10.2 ksi design. Torque on a lever-operated ball valve would probably be in excess of 40,000 in-lbs at full differential, and I doubt an ROV could manage that without the mechanical advantage of a geared operator.
3. I would expect you'd have fewer problems with the ball valve stem leaking over the long run than you will with the gate valve - that 1/4 turn operation does have the advantage of minimal impact on packing. In order to close the gate valve I'd think you would have to hope material (either corrosion or plants/crustaceans) hasn't built up on the exposed stem of the open gate valve, unless it's been sealed with some sort of bellows.
RE: Choice of Valves: Gate vs. Ball
RE: Choice of Valves: Gate vs. Ball
http://www.weirvalve.com/
RE: Choice of Valves: Gate vs. Ball
Velan manufactures ball and gate valves and has an awesome engineering group.