Use a ball valve

Firstly the valve will serve as block valve between the vessel and your (sand jetting) water system for which you should use a leak tight valve.

Secondly for 700psig you would need a Class600 valve which may exist but then probably will be just as expensive as a 600# ball valve.

Check API RP 14E which probably applies also for your facility:

section 3d Butterfly valves.
"Regular butterfly valves are suitable for COARSE throtteling and other applications where a tight shut-off is not required. It is difficult to accomplish a leak tight seal with a regular (non-high performance) butterfly valve. They are not suitable as primary block valves for vessels, tanks etc. Where a tight seal is required, use a high performance valve or limit the valve to low differential pressure and low temperature service (150F). Because low torque requirements permit butterfly valves to vibrate open, handles with detents should be specified"

regards
Mogens

Hmmm... by the client's spec. this is a 300# system. I agree with you, if this was a 600# system, but at this lower level I was thinking the butterfly vlv.s could work fine. We are NOT trying to throttle with these, they are either full open or full closed. I have seen them used on an automatic jetting system on a free water knock-out, worked slick there.   ...Mark

Most of the sand jet hookups around here (Calif. heavy) are standard ball valve and they work just fine.  Why would you want full port?  Unless your jetwater is grungy?  That would be overkill, in my opinion.  I've seen a few vessels with high-performance butterfly.  

I assume you have more than onbe jetwash point in the vessel.  Your jetwash header should be isolated at the vessel limit by a tight shutoff valve, so that will address Mogens' concern, which is a valid concern.

Thanks!
Pete

Sorry - this is a 300# spec required for 700psig
(I normally work metric units and looked at the wrong page of B16.5)

Anyway I still don't think these should be used.
Although I quoted the whole section from API RP 14E, of particular interest for you was this line:

"They are not suitable as primary block valves for vessels, tanks etc."

After all this is a recommended practice for offshore piping systems which I believe is what you are dealing with(?)

regards
Mogens

No ...actually this is oil field application (AK). BUT the jetting system I did see was in "Lost Hills" field near Bakersfield, CA. This was at a Heavy Oil Facility there ...That's been sometime ago, and I think it belongs to AREA now. OH, and yes there is a multiple point jetting system. THX for the help!!!  ...Mark