Gate Valve Seating Designs...

Solid Wedge Disc

The most widely used disc in gate valves - the solid wedge-shaped disc - with matching tapered body seating surfaces. Favored for its strong, simple design and single part.

Can be installed in any position without danger of jamming due to misalignment of parts.

Ideal for steam service, and well suited for water, air, oil, gas, and many other fluids.

Most practical for turbulent flow because there's nothing inside to vibrate and chatter.

Refacing of the tapered disc surfaces isn't easy, but there's little need for it is valve is used fully opened or fully closed.

Might be subject to some sticking when subjected to extreme temperature changes where body contracts more than disc. For such conditions, flexible wedge disc is recommended.

Double Disc

This parallel-faced double disc makes closure by descending between matching seats in valve body. As the valve is being closed, a lower spreader (or in some cases, a disc wedge) strikes a stop in the bottom of the body. Further closure brings the upper spreader into contact with the lower spreader so that the discs are forced outward against the seats.

First opening movement releases discs, and continued operation raises them clear of seat openings.

Widely used on water service, in waterworks and sewage disposal plants; also on oil and gas, in cross-country pipe lines.

Generally unsuited for steam. Rapid expansion and high velocity of steam flow tend to vibrate loose internal parts in disc assembly, hastening wear.

Exposure of closed valve to rise in external temperature may cause dangerous increase in internal pressure, if non-compressible liquid is trapped between discs.

Because discs and body seats are perpendicular and parallel, repairing or refacing to compensate for wear is easier than on a tapered wedge disc.

Should be installed with stem above horizontal for best results. Many spreader mechanisms are subject to jamming when installed with stem below horizontal line.

Their Service Characteristics

Flexible Wedge Disc

Developed especially to overcome sticking in high-temperature service with extreme temperature changes. The shape of the flexible disc can be likened to two wheels on a very short axle. The "axle" or spud at the center of the disc is amply strong to carry the two halves of the disc together at all times...and yet, it permits a degree of action between them. It is this "flexibility" that makes the disc tight on both faces over a wide range of pressures...prevents sticking during temperature changes, and assures minimum operating torque.

Although each disc face can move independently of the other...up to two full degrees...the construction is one-piece. There are no loose parts to cause harmful vibration.

Split Wedge Disc

A 2-piece, wedge disc that seats between matching tapered seats in body.

Spreader device is simple, and integral with disc halves.

When closing, last turn of handwheel forces discs against the seats. When opening, the first turn releases the discs from the seats.