Design of End connections of the valve

[vjr0512]

We are in the discussion of purchasing Knife Edge gate valves of sizes upto six inches dia to be used for On-Off purpose mounted with pneumatic actuator to be used in Sludge services. Valve manufacturers are offering Full lugged design valve only for this smaller size valve and indicating that above 500 mm size only they can manufacture Full Flanged design. Client is insisting for the Flanged design as this being Instrument valve.We know that these Knife edge gate valves are governed by the standard MSS SP-81. Is the Full lugged design is inferior to the Full Flanged design?

thanks to clarfy

 

[MGZmechanical]

It's very common practice for knife gate valves to be wafer or lugged. Even with full flange they're usually for wafer assembly.

 

[mk3223]

IMO, it's equally good for using either a lugged or flanged valves if using the proper bolting torque for the connections. However, the Client may prefer the flanged valve based on its operation and maintenance experience. Present your options to the Client and ask for the reasoning and/or preference.

 

[gerhardl]

Hi vjr52!

For knife-gate valves of some size, most factories will have 'steps' in increasing size where the model construction changes in type and availability, and also end construction and price. Such 'steps' could typically be around 300mm and/or 500mm.

It is not un-normal to have a supplier with this limitation, but in your situation I would double-check construction, quality and price from other suppliers for this size.

Most important for knife-gate valves are trouble-free construction: full tightness from both sides with or without pressure (end of line construction), without pockets where sludge can assembly, and top sealing that can be changed without taking the valve out of the line, correct orientation when mounted, and at size 500 supported by brackets to floor or wall (not by pipeline!).

If this is all OK end connections is not important, the valves can be fitted with fitting or extension pieces, and can if necessary function as end of line valves by maintenance.

By pneumatic knife-gate valves of this size it is especially important that the connection between pneumatic actuator-stem and knifeblade have 'non-firm' connection not to transfer contrary forces with a prolonged weight-arm to the blade.

Talking from long experience of knifegatevalves up to above 1000 mm I wish you good luck!