Globe check and stop check valves - pros and cons

[men8th]

Hi valve experts,

After scouring the internet and a couple of text books I have access to, I can't get a straight answer to this question.

Given a straight pattern (ie vertical spindle tee pattern) globe stop check valve, and a wye pattern stop check valve, what are the relative advantages and disadvantages. As far as I can tell, the only real thing to set them apart is that the wye pattern valve has a lower pressure drop, but might be more susceptible to having the disc/piston jamming if the service is dirty. The wye pattern valve might also take a larger flow rate to ensure the valve is fully open.

There must be more to it than that. Given that pressure drop is typically considered bad, and because you can't (shouldn't) throttle on a stop check valve, there should be no need for any more than the minimum possible pressure drop. For this reason, why aren't all globe stop check valves wye pattern? What is the need for the straight pattern valve?

Similar question for check valves. If the wye pattern globe check valve has a lower pressure drop, and pressure drop is considered wasteful, why is there a market for the straight pattern valve. Is there a substantial cost differential? Is one type more prone to valve slam? Is maintenance harder on one type than the other? etc etc.

 

[Danlap]

Hi men8th,

Check valve (Slam and Non-Slam) type are basically depending on its Closure Member: Swing, Globe, Piston, Ball and Nozzle
Y type was developed to perform as follow:
•Low pressure drop in very low pressure systems. This is due to the pattern profile
•Some may argue for Cost saving
•Combining the function of a stop valve with that of a throttling valve
However in the fouling service later found that
•The maximum valve opening still leaves a half-moon shaped port that easily traps dirt
•The Y-pattern orientation easily traps dirt, as its annulus is facing the flow. This may reduce the reliability of the Spring

I would argue your idea that pressure drop is typically considered bad. Kindly note that Check valve is for back flow preventer (and not a block or should not be considered as throttling valve), meaning that downstream pressure is (always) lower compare to upstream pressure.
Shall you are not sure that the medium is relatively clean, suggest to use the Straight type instead of Y-type.

Swing (slam) check valve normally comes starting from 3 in and above. And used in horizontal pipelines or at some cases in vertical pipes when the flow is upwards

Maintenance of check valve preferably to be done off-line in order to perform testing. However in most cases (welded end, short duration of shut down, etc.), minimum things can be done is unbolted the cover and clean the spring and closure member. This make Bolted cover check valve of any type maintenance strategy is equal.

Regards,
MR






All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[men8th]

Thanks for your considered reply Danlap.

The system in question has a very high turndown ratio. I wonder if you have any guidance on sizing. (I wrote another post so apologies for asking the same question here.)

I'm concerned about valve flutter/instability at low flow rates, but at the same time, I don't have much pressure drop to play with. To prevent flutter/instability at low flow rates, the literature I've read suggests that I should use a straight pattern valve. A straight pattern (ie piston) check valve will be fully open at lower flow rates. However, a straight pattern valve will also drop more pressure at higher flow rates, and I don't have that much margin in the system design...

 

[Danlap]

Hi men8th,

No, I don't have guidance on sizing. Sizing a Check valve (Non Return Valve/NRV) depending on many factor, too name a few that pops up almost every time is:
- Installation orientation, is it Horizontal or vertical. At some point, NRV will be gravitational assisted (by Spring or in larger size by Closure member weight). Having installed NRV vertically with low flow rate, low DP may prone to chattering of the NRV itself
- Pressure Drop desired. This can be empirical (by calculation) and or by simulation. Some advance manufacturer can do this
- Flow rate and Real Operating pressure will make the sizing more precise
- Cracking pressure required (desired pressure when NRV start to Open)
- Process condition, do you put double jeopardy factor into consideration? Is the flow relatively streamline or turbulence? etc.

In terms of sizes.
Ball/Piston is normally in sizes from DN 15 to DN 50; Swing normally start from size DN80 and above; Dual Plate check valve normally start from DN300 and above

In terms of Pressure drop from the worst to the least worst is: Piston/Ball (either Straight or Y pattern)> Dual Plate check valve > Swing type
Why? best practice that normally used for Pressure recovery are:
Le: required nominal length for Pressure to recover after "obstructing" closure member.
D is nominal Diameter of the NRV
[ul]
[li]Swing type Le is 50D[/li]
[li]Ball or piston type for DN 40 (NPS 1 ½) and smaller. Le is 135D[/li]
[li]Dual Plate type Le is 75D[/li]
[/ul]

For other type that I am not mentioned above, the pressure drop and other data shall be taken from the data obtained from the equipment Manufacturer/Supplier.
This is non standard service which may cost you extra, but its worth to ask/inquire. My gut feeling solution for your problem is Nozzle Non-Slam check valve. But maybe I am wrong

Regards,
MR



All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

 

[men8th]

Thanks for your kind reply. I'll continue to pursue this with the manufacturers we have on our approved vendor list. To be honest, I'm not getting much help from them beyond "you might want to put it on a flow bench and check the performance before you install in the system"...

 

[Danlap]

Feed the manufacturer (AVL is different with AML), with parameter as follow: Upstream and Downstream pressure, desired maximum Pressure drop, start up flow rate (to determine cracking pressure), actual Operational flow rate, viscosity and density of your medium. Choose manufacturer that can fabricate most of NRV types (Slam and Non-Slam type).
The answer to your question will cost you more than the price of valve itself for sure (if we're talking about small sizes). Since most manufacturer have develop their own calculation and or software, most likely the answer would be in pdf and curve show curve of Flow rate vs pressure rating OR table of values with different scenario.

If the answer remain the same "you might want to put it on a flow bench and check the performance before you install in the system"..., then you're dealing with manufacturer that produce (with all due respect) a Low end type only e.g. Swing check valve.

Good luck

Regards,
MR
nosuchvalve@gmail.com


All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected