Pressure Seal Valve 1

[cranekiran]

Dear all,

I would like to know what are the Important Design Parameters for designing a cast steel pressure seal valve say a 600# to a 1500#?
Thanks in advance.

 

[owlscreech]

Assuming you have knowledge of other aspects of cast steel valve design, the focus would be the pressure seal area. The following should be considered:
1. Method of pressure seal ring retention, i.e., how the load from the upward bonnet force is transferred to the upper part of the body. The simplest method is to use a metal ring which is inserted into a groove machined into the body. The metal ring is cut (segmented) to allow the ring to be placed into the groove.
2. Stress considerations include analysis of the groove to insure that both the sheer and torsional stresses in the body remain below material limits. Roark has methods for this. Similarly the ring requires the same analysis using Roark models.
3.The pressure seal gasket usually is a relatively soft material or a hard material with a plating that conforms to the body bonnet interface. Some manufactures sometime use an additional ring on top of the segmented ring to prevent deformation of the pressure seal ring by the segmented ring.
4.The angle of the pressure seal ring wrt the bonnet is important also. The is usually about 1-2 degrees achieved by using bonnet to pressure seal ring angle differences.
5. Typical bonnet angles run about 20-25 degrees from the vertical (meaning that the corresponding ps ring surface is about 18-23 degrees. The outside of the ps ring which is contact with the body wall typically is not machined with any angular differences, since that seal is depended more on the dialation of the ps ring by the wedging action of pulling up the bonnet which has pushed the ps ring into the segmented ring.Pull-up studs are usually used for this purpose.
6.The usual clearance between the OD of the bonnet and the ID of the body is 15 mils while the ps ring od to body id is about 8-15 mils with the smaller the better. If you get it much smaller, there may be assembly difficulties.
7.The area where the ps ring contacts the body should be SS overlaid, e.g., 309, and have a finish around 32 rms.

 

[cranekiran]

Dear O.S,

Many thanks for the reply.Actually,pressure seal gate valve is new to me therefore the input provided is valuable.
kindly tell me what is the Roark method?Also,What are the design considerations for the contact between the wedge (disc) with the seat ring.Is it important that the hardness of wedge should be about 50 b.h.n less than the seat ring's hardness as someone told me?I also noticed in some websites that the body has a hole drilled till the segmented ring;My guess is that it for removing the segment ring.I also noticed that all pressure seal gate valves irrespective of different manufacturers maintain the same material of construction and looks too.
Thanks in advance.