Angle Seat Piston Valve vs. Pneumatically Actuated Ball Valve?

[adammil1]

We are currently designing a system that is a little bigger than what we have done before and now are into a whole new class of valves. The system needs to be pneumatically controlled for explosion proofing requirements. The medium is ultra pure DI water with dissolved gas in it and rather chemically aggressive, but otherwise very clean water. At the present time we are trying to decide on what type of valve to use for simple on/off flow regulation.

Most all vendors so far have been recommending pneumatically actuated ball valves with one exception who is recommending an "Angled Seat valve" like the one below.

The actual operation of the angle seat valve seems rather straight forward, while there is some added pressure drop there as opposed to a ball valve for our needs I am not sure that it matters. So outside of that why wouldn't we want to go with the angle seat valve as opposed to a ball valve? The angle seats so far seem to be a bit cheaper too.

Unfortunately we just don't have the experience needed to make a good judgement call here.

 

[LittleInch]

I'm taking an assumption here that there is a required flow path from Left to right in your photo.

My conerns over this type of valve would be
1) Assuming L to R flow, clearly seating force is dependant on spring force. Excess pressure over that stated on the data sheet will open valve (like a relief valve)
2) For flow R to L, excessive flow disturbance and opeing force may be very big compared to fluiod pressure keeping it closed
3) Rapid closure over many cycles inroducing cracks into valve seat
4) Sealing area seems metal to metal - Ok for waer but not so good for sealing
5) Potentially very rapid closure ( unless you throttle the air discharge) meaning potential hydraulic schock and vibration into the pipeing system leading to fatigue
6) Seals need to accomadate a sliding motion, which is a lot harder than a rotational motion and hence potential for leak is increased

Otherwise looks a nice valve....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[btrueblood]

LI,

I think those valves can flow in either direction, and (should) have elastomer seats, if like the ones in the data sheet below. We've used similar for control of a low-pressure flow (water+glycol) for several years with no issues. You are right about the rapid closure, but that is desirable for our purposes, and the flow rate/differential pressure is controlled to avoid water-hammer shocks.

http://www.thevalveshop.com/menu/auto/asco/8290_datasheet.pdf

 

[adammil1]

My conerns over this type of valve would be
1) Assuming L to R flow, clearly seating force is dependant on spring force. Excess pressure over that stated on the data sheet will open valve (like a relief valve)
2) For flow R to L, excessive flow disturbance and opeing force may be very big compared to fluiod pressure keeping it closed
3) Rapid closure over many cycles inroducing cracks into valve seat
4) Sealing area seems metal to metal - Ok for waer but not so good for sealing
5) Potentially very rapid closure ( unless you throttle the air discharge) meaning potential hydraulic schock and vibration into the pipeing system leading to fatigue
6) Seals need to accomadate a sliding motion, which is a lot harder than a rotational motion and hence potential for leak is increased

#1: Clearly this is the case, we actually do have an area where running this thing like a smart check valve would be ideal, but you are correct orientation to flow is very important with these valves.
#2: I would think on this one we would defer to manufacturer's recommendations, I know that the ones I was looking at were good to 40BAR or so DP for opening and closing, others only 150psi I think it should just be an issue between air pressure in the cylinder, vs pressure area acting on the seat.
#3: Do you have any experience with seat cracking on these over several cycles, along this route the valve I was planning on going with would be 316SS on teflon for the seating arrangement? I would think the softness of the Teflon would help to prevent against this issue.
#5: This is something I hadn't considered I will have to discuss the air discharge with our pneumatic people.
#6: I see where you are coming from there but when it comes to a Ball valve, there is a heck of a lot of sliding area in contact with the seals on the face of the ball too. I guess the question would be what do people see when it comes to actual fielded service of these?

Anyone here use them commonly, clearly ball are far more common then this type so I wonder if it is for good reason.

 

[LittleInch]

adammil,

#3, To be honest no II don't, but I was just looking at the design which seems to have only a small unsupported lip to seat against and the top side and it would seem inherently susceptible to fracture over time. Soft closure will help which is why L to R dlow looks much more favourable, especially if you're talking about shutting off moving fluid. Many valves are really only designed to isolate and not close against flow or open against large Differential Pressure - if that's your duty then you really need to be up front with the suppliers and tell them what your flow rate / velocity is that you want to close against and how often it needs to do this in it's lifetime. You might get a bit more "squirming" when you ask them guarentee their valve for thousands of closures against moving fluid / opening against large DP.

#6 I meant seals against fluid escaping to the outside. Gate valves have this issue as well, but ball valve external seals only rotate the shaft compared to this type which is sliding up and down to prevent your contents escaping. If you have nice clean fluid, then ball valve seats, especially metal seated ones are quite good. If the seats are plastic or have lip seals then they won't last if you're closing against flow and with large DP on opening - see #3 above about telling vendors what you're using it for.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way