Cryogenic Globe Valve Flow Direction 1

[mechconst]

Can the flow direction on this type of globe valve be in either direction? The service is liquid oxygen with this valve located on the upstream side of the liquid oxygen vaporizers. There is a flow arrow on the side of the valve, but why would it matter if the flow is pushing up on the disc or down on the disc?

 

[Albator]

It is probably due to the design of the valve, which prescribe no leakage in a particular direction.

The pressure of the fluid may be used to push down the disc against the seat, to have a zero leakage capability in that direction, which would not be true if the fluid tends to take the disc from the seat.

 

[JLSeagull]

Discuss the specific globe valve model for review with the manufacturer. If this is a traditional globe valve, the velocity between the plug and seat can cause a bath-tub stopper affect that slams the plug into the seat due to reduced pressure when operating less than 10% travel. This may not be an issue if the valve is balanced like a cage valve. Many globe style valves have a recommended orientation and work satisfactorily in both directions.

 

[tsenthil]

A Piston Actuator can be used in a unbalanced trim to counter Bath Tub Stopper effect instead of standard Spring & Diaphragm actuators. However if your liquid is cavitating and valve manufacturer uses a muli Hole anti cavitation cage, the flow to be happen over the plug. They ideally want to flow the liquid from outside the cage to inside allowing liquid streams to bombard each other for killing the high energy.

 

[insult2injury]

Additionally, if it is flashing, the preferred flow is generally the opposite of that for the cavitation case.

I2I

 

[JimCasey]

Or if it's just a garden-variety manual globe valve, the flow is from under the seat so that there is minimal pressure against the packing when the valve is closed.

 

[tsenthil]

Even for Flashing, i believe the flow direction should be similar to cavitating service as inlet in only liquid. For Flashing we higher size valve or higher Cv required to handle gas expansion in the downstream.

 

[insult2injury]

Typically, trim designed for flashing service is similar to compressible flow trims, not incompressible such as liquid and cavitation trims. With anti-cavitation trims, the vapor bubbles are maintained in the inner cavity so their collapse is located away from the trim solid parts susceptible to cavitation damage; however, for flashing service, the vapor fraction is sustained in the flow.

I2I

 

[tsenthil]

Now i think that flow direction dont have any significance in flashing application. What we need is only a Hardened Trim to counter erosion due to Flashing. May be an Angle valve with Hardned trim will help in eliminating Erosion damage.

 

[insult2injury]

Hardened trim (and other valve materials such as the stem, etc.) is standard for most flashing applications. Depending on the application, multistage trim may be used as well. For noise control, etc., the flow through the valve typically follows the same rules as compressible flow.

I2I

 

[ValveEngineer123]

mechconst: With respect to determining the correct flow direction, more information is required.

Is this valve in an isolation or control/throttling application? For isolation, I agree with JimCasey, flow under the seat will isolate the packing from system pressure, however this is only true for an unbalanced plug (which you would likely be using if it was an isolation application)

Is it a balanced or unbalanced plug?

What type of actuator is installed on this valve (pneumatic spring-diaphragm, pneumatic piston, electric, manual gear operator, top mounted handwheel)? For a top-mounted handwheel or gear operator, the bathtub stopper effect is not an issue.

tsenthill/I2I: With respect to the flashing/cavitation discussion, quote "With anti-cavitation trims, the vapor bubbles are maintained in the inner cavity so their collapse is located away from the trim solid parts susceptible to cavitation damage"

Is the purpose of anti-cavitation trim not to limit the pressure drop through the cage to small stages such that vapour bubbles never form at all, and thus, never collapse?

 

[insult2injury]

ValveEngineer123: Yes, that is the design strategy for most multistage trim; however, for lower levels of cavitation, the trim may be designed to allow cavitation in the interior space without inflicting damage to valve. This is often a less costly design as single or lower number of stages are required. Most severe duty control valve manufacturers have designs for both and select the best trim based on the cavitation coefficient and price.

I2I

 

[tsenthil]

I2I: Noise in Flashing duty.. Is there is anyway to find Noise produced in Flashing application? I normally made some correction in Vapor pressure to make the application cavitating and find the noise and presume noise produced in Flashing is less than Cavitating service. Most of the case i end up in noise less than 85 dBA. Is this correct?

Also i was told that Multistage trims used in flashing service to reduce trim exit velocity.

 

[insult2injury]

Yes, reducing exit velocity reduces noise. In order to reduce the velocity, the flow area needs to expand in the direction of flow. Correspondingly, this is why the fluid flow outward through the cage as there is greater available area at the trim exit. If the fluid were to flow inward through the cage, the flow path at best maintains a constant flow area but generally contracts. For instance, if you had a cage with a 1 inch ID and 3 inch OD, the outer circumference is 9 times larger than the inner circumference.

I2I

 

[mechconst]

The valve is used for isolation of each vaporizer. There are three vaporizers in parallel, with a globe valve on the upstream side, and a motorized ball valve on the downstream side.

 

[insult2injury]

The valve may seal effectively with flow in the opposite direction; however, the manufacturer should be contacted to verify. If this is a y-pattern valve, you probably wouldn't want to reverse the installation even if the manufacturer said it could seal.

I2I