DIAPHRAGMACTUATED VALVES

	DIAPHRAGM ACTUATED VALVES	RAF MODELS	RAF General Information
\| Description \| Applications \| Available Models \| Installation \| \| Typical Application \| Specification Form \|	RAF 88 Surge Anticipating Valve

Description RAF 88 is adjusted to eliminate hazardous pressure surges typical of water hammer conditions. A water hammer is caused by an abrupt shutoff of a pump or rapid closure of a main valve, causing a fast propagation of low pressure front, followed by an extremely high pressure back-wave. A series of pressure waves, each one composed of alternating low & high pressure, is created within a few minutes.	RAF 88 is a piloted hydraulic valve activated by line pressure. The valve has two pilots, for high & low pressure. Under normal conditions the RAF 88 is closed. It opens when the line pressure drops below a preset pressure, in anticipation to the following surge, & remains open until the fluctuations subside.
Applications RAF 88 - General Application two-way surge anticipating valve. Pressure rating up to 16 bars.	Available Models Use a surge anticipating valve to protect water lines against water hammer damages. Uphill supply lines of considerable length & large diameter pipes are more susceptible to water hammer damages. For more info or hazard analysis of particular network consult Raphael Engineers.
Installation RAF Surge Anticipating hydraulic Valve is activated by line pressure & controlled by two pilot valves. Both pilots include spring-loaded membranes. The low pressure pilot (the left one in the drawings) is preset to open the RAF 88 gradually when the line pressure drops about 10m below normal. The high pressure pilot (on the right) is preset to open the RAF 88 when the line pressure rises about 10m above normal. The RAF is normally closed. Only when the line pressure is drops below or rises above the preset limits, the RAF 88 is piloted to open. A water hammer event starts with a considerable pressure drop, which cause the RAF 88 to open. Then, as the water wave rolling backward, the valve remains open & let the pressure out to diminish its impact.
RAF 88- control mode Manual: To open the RAF 88, close cocks 1,2 & 4 & open the Vent. Automatic: The RAF 88 is normally closed. Ensure that all cock valves (except the vent) are fully open. Normally, line pressure is higher than the set point of the low pressure pilot (the left one), but lower than that of the high pressure pilot (the right one). Thus, ports 2 in both pilots are closed. There is no flow from the main line to the pilots. The RAF control chamber is connected directly to the line pressure through needle valve a. The RAF is closed. When line pressure drops below the lower set point, the spring of the low pressure pilot (left) push the pilot’s membrane downward & on the way opens port 2, as shown in the drawing. The right pilot does not change. The RAF control chamber drains out through port 2 -Vent b of the left pilot. The RAF 88 opens in anticipation to a surge. The pressure drop is soon followed by a surge which reclose the left pilot but opens the right one ( the high pressure pilot) at the same time. The RAF control chamber now drains through ports 2-3 of the right pilot & thus remains open. The high pressure wave is allowed to flow through. After the surges subside, & the line pressure return to normal level, both pilots reclose & the RAF 88 follows suit. Typical Application RAF 88 is located next to a booster pump to protect the supply line downstream of the pump from water hammer damages.		RAF 88 Surge Anticipating hydraulic Valve Adjustment Use needle valve a-b to control the RAF operational speed. Adjust the low/high pilots set points by the adjusting screws. See list of available springs on the next page.

Standard RAF 6300	Special Features
Complete basic RAF valve as specified above	Enamel/epoxy coating
Self-cleaning screen filter	External heavy duty screen filter
Two metal pilots (2-way)	-
60 mm pressure gauge	Pressure checkpoint
Four cock valves	-
Needle valves
3/8" reinforced plastic tubes	Copper or stainless steel tubes