Clean Compressed Air Brochure - 14694 SOFT START/DUMP VALVES EXHAUST AIR

The next form of protection is that associated with the moving parts of the system, where the parts themselves can need protection against excessive wear due to loading on start up or there is danger to personnel fromsudden movement of the parts.Here the use of“soft start” (“slowstart”) valves is desirable. The normal operation is to allow air to pass to a pneu- matic system or device in a gradual manner, where the rate of pressure build-up can be controlled by adjustment of the valve. The valve design is generally an internal poppetvalve which is spring operated and when thegradual pressure build-up produces a force in excess of that holding the poppet closed, the poppet moves to the open position allowing flow to proceed through the normal flow passageways. The level at which the poppet operates is called the snap point and for most devices this snap point will be in the range of 40 to 70% of full line pressure.Because pressure build up in anysystem is dependant upon the system volume it is important to locate these devices close to the piece of equipment they are to protect. Fitting of a larger valve to a complete distribution system will generally mean the system will take many minutes to fully pressurise.It is extremely common to couplethe slow start valve with a dump or exhaust function valve within one body, for compact- ness.The function of the ‘dump’ valve is toquickly exhaust the pressure from the downstream system. The valve can have solenoid or air pilot operators and often a manual override or emergency dump function.Legislation Reference:BSEN9835.1.4 Exhaust air needs to be treatedcorrectly to reduce the effects of noise, oil mist and to minimise danger to personnel.Where a dump valve is employed,large volumes of air can be released at highspeed which will produce high noise levels.Simple silencers made of porous materials are often able to deal with this. In more demanding high velocity cycling applications a heavy duty silencer may be needed.Silencers are normally rated for theirnoise reduction and associated back pressure so the choice should be dependentupon the duty required of the device toensure the most cost efficient silencer is utilised.The next major pollutant is oil. Allpneumatic lubrication systems are total loss systems, the lubricant goes into the system, gets degraded in its function and is carried along with impurities and dirt to the atmos- pheric exhaust.In well maintained and correctlylubricated systems of a general engineering nature the amount of exhausting oil is very small and will disperse without generally affecting the working environment adversely. However incorrectly lubricated systems or those which require high levels of lubrication for heavy duty applications can expel high levels of oil into the atmosphere on their