船舶管系、阀门等介绍.ppt

CHECK VALVES Some are automatically operated with no hand wheels or stems and some have the capability of being shut off. Used to prevent return or back flow Several Types Lift Check Swing Check Ball Stop Check Valves (can be positively shut off) * * BALL VALVES Quick opening (1/4 Turn) Excellent for full flow applications Can also be used for throttling The fluid flow acting on the partially exposed ball can cause erosion. High pressure ?plug valve * * STRAINERS Prevents the passage of grit, scale, marine life, and other foreign matter that could obstruct pump suction valves, throttle valves etc Baskets can be removed for easy cleaning. Simplex — only one basket, flow must be stopped to clean Duplex — two baskets — flow may be diverted to allow cleaning of off-line strainer Y-Strainers * * STEAM TRAPS ?Steam traps are used is systems to Drain condensate from heat exchangers They hold steam in heat exchangers until it has completely collapsed to condensate. Allows latent heat available in steam to be exchanged They are used in low points of steam piping systems help avoid water hammer Three main functions of steam traps are Allow condensate which was steam to collect and flow back to the condensate system. Vent air and other gases Prevent the escape of steam- loss of available latent heat. * * STEAM TRAPS AND PIPES A steam trap is an automatic valve it senses the difference between steam and condensate. The trap discharges the condensate with little or no loss of steam, which contributes to high operating efficiency. Steam traps are divided into three main groups: thermostatic mechanical thermodynamic * * THERMOSTATIC TRAPS It measure temperature The balanced-pressure thermostatic trap has a liquid-filled bellows that expands and contracts. When steam is in contact with the bellows causes the bellows to expand closes the valve If condensate or air is in contact with the bellows, bellows contracts and condensate is discharge