Valve direction

[LSUUR]

I have an arguement with our customer about valve flow direction.
Our ball valve has uni direction and flow mark on the valve body and valve will be leaked in reverse flow.

Our skid has 2 vessels, one is working and the other is stand-by.
As you can see attached file, flow direction is red arrow at valve open condition and we wanna install valve according to flow direction at valve closed condition.
however our client valve shall be installed according to flow direction at valve open condition.

Could you advise flow direction definition for valve installation?
If we install valves according to flow direction at valve closed condiion, how can we convince our customer? is there any reference or documents to install valve?

Flow direction on valve body means direction at valve open condition?

Your kind advice would be highly appreciated.

 

[KoachCSR]

The flow direction on the valve body typically corresponds to flow through the valve when open.

 

[Danlap]

Hi,

Without giving any details (assuming you cannot share GA drawing of the ball valves), what makes your ball valve uni-directional?

Will not go to basic of single or double piston effect or valve design, but in general Ball valve can be bi-directional, uni-directional, or bi-directional but have preferred direction. In close position.
In general bi-directional BV in close position, can handle shall maximum design pressure might come from either upstream or downstream side. And it will still have same (and guaranteed) leakage rate. This is typical for Trunnion mounted ball valve
Bi-directional BV with preferred direction basically has the same concept, but usually since cavity is ‘exposed’ to the pressure therefor Delta P is not in favor for example to ‘push’ the downstream Seat against Ball. This is typical for Ball valve with cavity relief drilled to one side of the ball. One may argue but I think floating ball valve also part of it.
Uni-directional ball valve by concept is manufacturer cannot guarantee that shall pressure applied from the other side or mistakenly (or deliberately) BV is installed on reverse direction of preferred arrow, ball might be tight and not passing to another side. This is typical for single seated ball valve for severe service and/or tight shut off application. Usually the tolerance between Seat and Ball is really tight by means of spring energized seat whatsoever. And end-user already pre-determine the flow e.g. due to gravity (hazardous) and P/T rating, therefore end user do not need the other side to be tight since pressure will not go the other way. Rising Stem Ball valve also part of this category, e.g. used in PIG launcher. As one don’t really matter if the nitrogen purge from PIG launcher leak to the pipeline, thus RSBV will be uni-directional and to be installed with arrow facing to PIG launcher.

Which category are you?
I see you are highlighting double block (no bleed) configuration, and there are some predefined scenario. Maybe end user would like to do maintenance on the main (middle) line when valve in close position, or filter 1 should be pressure free when filter 2 is in used, etc.
Break down those scenario together with the end user and come to an agreement which side should be “pressure-less” when valve is open and close. I am positive you will land into some middle ground.

By skim reading the scenario, maybe I am wrong, but it is wise to add Pressure Gauge between double block and valve to be installed arrow facing one another. Once pressure gauge is OK (pressureless or pressure is not increased) it might provide justification to that other side is ‘safe’.
Some end user who deals with process and safety on daily basis often do not speak valve language, but they assess risk from other point of view.
Better expert in this forum might fine tuning my explanation over valve design above.

Regards,
MR

https://nosuchvalve.com

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

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[LSUUR]

Thank you for the reply.
valves are used for cryogenic condition and cavity relief and floating ball type.
Is there any requirement valve installation direction in the rules or codes?(such as valve shall be installed as per flow direction or etc.)

 

[Danlap]

There is no rules or codes for installing valve as per flow direction. It is based on principal (end user - valve guru in combination with safety - etc.) preference.
Check valve uni-directional open position. Self explanatory, upstream flow cannot pass shall valve reversed.
Globe valve uni-directional (usually flow under) open position with some exception for bypass around discharge check valves of spared centrifugal pumps. Again this is principal suggestion. Why my company allowing this, since spared pump in order to be kept warm it needs to see small flow (passing through) break opened globe valve, and preferably this valve is flow under with respect to the 'active' pump.
In general wherever possible, body cavity relief should be to the upstream side of the valve.

Your floating ball valve with cavity relief is bi-directional when opened, and preferably uni-directional when closed
I understand your concern that there might be cryogenic medium trapped in the cavity, and should this is 'warmed-up' the medium might change phase and 'damage' the valve e.g. seat.

Having said that, I understand end user point of view. In general it requires approximately 2 bar for an upstream medium to be able to 'push' relatively small sizes floating ball valve to seat properly against downstream seat.

So for example: from filter 2 goes to double block valve (your bottom picture), and first valve is internal passing of let say 1 bar. Then the second valve is not functioning as blockage, since it has cavity and at 1 bar it will not seal.

Both of you and end user are correct. Since end user is the one who write the operational protocol e.g. which valve open and on what sequence, then you should land on an agreement and do some risk assessment. Is risk of thermal cycling (inside cavity) bigger than risk of passing?

Regards,
MR

https://nosuchvalve.com

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

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[mk3223]

In the cryogenic service, I suppose that the ball vale is uni-directional because it has a vent hole on the internal ball to relive the cavity pressure to the process side. IMO, these ball valves should be specified with the "PE" on P&ID to show the uni-directional function.

 

[Ehzin]

Assuming the valve construction allows only effective sealing in one direction, I feel like it should be self explanatory why you want the sealing direction to preferentially isolate the filters. Maybe explain that it's not preferred flow direction, it's effective sealing from high pressure to low pressure system. When a filter is isolated and vented, it becomes the low pressure system. The common line is now the high pressure system. Assuming the arrows reflect a high pressure to low pressure orientation, you want both the upstream and downstream valves' arrows pointing at each filter. This way neither valve will leak your process into a filter while it's isolated. Both of the valves in the center should flow downwards on the P&ID in my opinion. The high pressure to low pressure orientation should always be in this direction and the two valves shouldn't complete or lock valve in them.

As a comment, I may be unfamiliar with floating ball valves but I thought they didn't really have much of a cavity to lock any process in. The ball floats in a chamber and relies on line pressure to push it to one seat. In what way is a cavity formed in this type of design? Maybe I need to brush on my floating ball designs.

The only thing to keep in mind is that you're PSV should be sized to vent off any boiling cryogenic liquid in the filter. Until you vent the filter, you can generate boiled vapor due to ambient temperatures or other source. Depending on the insulation and temperature of the liquid you could generate a non-negligible amount of vapor that could lead to overpressure without a proper relief device.

If the scope of your project is to design a skid or equipment package and it's simply using a common ball valve like a Velan/Kitz/etc... I feel like you should be able to give more specifics of the valve. Are you the valve fabricator or are you just buying a somewhat common valve and installing it as part of some equipment?

Thanks,
Ehzin