Special Constructions

Full flanged uni-directional knife gate valves

VAAS offers a limited range of sizes of the FIG 940/950 models in a full flange version called model FIG 952. All internals and ratings remain similar to the basic 940/950 valves.

Full stainless steel constructions

For very corrosive environments, VAAS valves such as model 940 and 950 can be offered in an “all stainless steel” construction. The handwheel is generally standard (cast iron, painted)

Hardfacing Options

Knife gate valves can be offered with many hardfacing options to make them more suitable for handling abrasive media. These processes generally involve treatment at high temperatures and could result in some warping of parts and therefore, leakage capability of valves with these options will be lower than MSS SP-81 requirements. Typical options are:-

Stelliting of gate edge and/or seat surfaces – This is a weld deposit process using Stellite 6 welding rod to a depth of approx 1mm and typical hardness of the surface would be 300-350 BHN.

Nitriding This process produces a thin layer (typically 20 micron) of nitride on steel and stainless steel base metal and can be applied on valve body and/ or gate. This process is generally suitable for services involving sliding wear (as in handling dry powders etc).

Hardcrome plating This is a hot dip process producing a uniform hard layer on steel and stainless steels
Spray & plasma deposits – These are also possible options for special service requirements

Purge connections

Knife gate valves can be provided, as an option, purge connections at different locations of the body. These are used to clean the seating areas and/or chest area (area below the packing) where media could settle in some applications. Purges are usually provided at 3'o clock, 9'o clock positions and/or on either side of the chest pocket. Very severe services may warrant more purge ports and same can be provided as required.

 

 

 

V-Orifice seat for Throttling / Control applications

Standard round-port knife gate valves are used only for on/off applications and are not suitable for throttling services. However, Uni-directional valves (model 940 & 950) are also available with a v-orifice seat option. This is used for throttling and control applications and the v-orifice seat provides a “modified linear” control characteristic. These valves are also used with pneumatic actuator and positioner for operation from a control signal. VAAS can assist in sizing the valves for such services.