Pulsation dampeners (accumulators, surge suppressors) are used to control and minimize the pulsations that result from a pressurized system’s stroking action. They increase system efficiency, performance, and pump life; decrease maintenance costs and down-time; and protect pipes, meters, valves and instrumentation from pulsation, vibration, and hydraulic shock. Most pulsation dampeners use a bladder or bellows to separate the process fluid from a compressible gas. During the pump’s discharge stroke, fluid pressure displaces the bladder or bellows and compresses the trapped gas. During the following cycle, the momentary interruption of fluid flow causes the compressed gas to expand, forcing the bladder or bellows to push the accumulated fluid back into the discharge line.
Types of Pulsation Dampeners
There are many types of pulsation dampeners. Adjustable dampeners can be set or tuned to accommodate different pressure ranges and response rates. Automatic dampeners use a valve in the device’s non-wetted section to allow increases in air pressure to balance increases in liquid pressure. Chargeable dampeners fill a chamber with compressed air or nitrogen gas to create a cushion that absorbs pressure pulses within the system. By contrast, liquid-filled pulsation dampeners use a fluid-filled cavity to smooth the system. Suction-lift dampeners provide a stabilizer on the inlet side of the pump to reduce acceleration and ensure even pump feeding. Pressure snubbers are positioned before a pressure gauge to provide protection against pulsations in the measured media.
Specifications for pulsation dampeners include maximum pressure, capacity, inlet size, and inlet type. Many suppliers specify maximum pressure in pounds per square inch (psi) and capacity in cubic inches (in3). Inlet size is usually expressed in inches (in). There are several inlet types for pulsation dampeners. Flanged inlets have multiple bolt holes for mounting to a mating flange. Threaded inlets have a threaded connection, usually a pipe thread. Tri-clamp dampeners have a specially configured flange that fits a clamp.
Pulsation dampeners use bladders or bellows made from a variety of materials. Buna-N provides good resistance to petroleum hydrocarbons and fuels. Ethylene propylene (EPDM) offers good resistance to sunlight, weather and ozone. Chlorosulfonated polyethylene (CSM) provides excellent resistance to ozone, oxidation, sunlight, and weathering. Neoprene is used over a wide temperature range and displays outstanding physical toughness. Polyvinyl chloride (PVC) has good flexibility, a smooth surface, and nontoxic qualities. Because of its inert nature, some PVC grades are used in food and chemical handling applications. Polytetrafluoroethylene (PTFE) is an insoluble compound that exhibits a high degree of chemical resistance and a low coefficient of friction. Silicones are polymers that provide heat, cold, and weather resistance; electrical insulation; good release; and water repellency. Many proprietary products are available.
Selecting Pulsation Dampeners
Selecting pulsation dampeners requires an analysis of housing materials. Acetal polymers offer excellent lubricity, fatigue resistance, and chemical resistance. Polyvinylidene fluoride (PVDF) is a melt-processable fluoropolymer with better strength and lower creep than other fluoropolymers. Polypropylene is a thermoplastic material that exhibits excellent cold flow, bi-axial strength, and yield elongation properties. It is similar to PVC but can be used in exposed applications because of its resistance to UV, weathering, and ozone. Other housing materials for pulsation dampeners include aluminum, brass, cast iron, carbon steel, and stainless steel.