Valves

There are a large variety of valves and valve configurations to suit all services and conditions; different uses (on/off, control), different fluids (liquid, gas etc; combustible, toxic, corrosive etc) different materials and different pressure and temperature conditions. Valves are for starting or stopping flow, regulating or throttling flow, preventing back flow or relieving and regulating pressure in fluid or gaseous handling applications. Common valve types include: Ball,Butterfly,Check, Diaphragm, Gate, Globe, Knife Gate, Parallel Slide, Pinch, Piston, Plug, Sluice, etc.

The following types of valves are used in a variety of applications, these descriptions may provide a basic guideline in the selection of valves.

BALL VALVES

Because of their excellent operating characteristics, ball valves are used for the broadest spectrum of isolation applications and are available in a wide range of sizes and materials and are available in full fl ow and full through conduit. Advantages – quick acting, straight through fl ow in either direction, low pressure drop, bubble tight shut off & operating torque, easily actuated. Disadvantages – temperature limitiations on seating material, long “relative” face to face dimension.

The butterfly valve derives its name from the wing-like action of the disc which operates at right angles to the fl ow. It’s main advantage is a seating surface which is not critical. It is designed for fl ow isolation. The disc impinges against a resilient liner to provide bubble tightness with low operating torque. Compact and with a simple construction, butterfly valves facilitate easy pipe arrangement. Due to disc, they have slightly reduced fl ow characteristics. Advantages – quick acting, good regulating characteristics, compact & light, low pressure isolation. Butterfly valves are simple, reliable and range in size from 40mm to 1000mm and beyond. They can be controlled by a notched lever, handwheel as well as by pneumatic or electric actuator. A shaft turns a disc 90º within a pipe. The disc angle within the pipe can provide a restriction varying from drip-tight through to almost full fl ow (except very small sizes).

Sometimes referred to as a non-return valve, the check valve prevents back-flow in the piping by constantly keeping fluid flowing in one direction. Check valves operate automatically. Some piston/disc check valves are spring loaded for fast operation, (minimum cracking pressure should be specified). Vertical downwards flow requires a spring loaded check valve.

Swing Check Valves: – Swing & Wafer checks cease reverse flow with a flap that swings onto a seat. Use swing checks only for forward flow that is horizontal or vertical upward.

Piston Check Valves: – Piston & Spring checks cease reverse flow with a spring loaded plunger.

Ball Check Valves:– Ball checks have a ball that slides into a hole as forward flow slows. Consider a ball check for semi-solids such as pulp or effluent.

Titlting Disc Check Valves: – Tilting Disc check valves are similar to Swing check valves but in most installations, slamming is minimised upon reversal of fl ow so noise and vibration are reduced.