33 Raphael SAV Brochure

RAF
RAF 88
G E N E R A L P U R P O S E H Y D R A U L I C VA LV E S
S u r g e A n t i c i p a t i n g C o n t r o l Va l v e
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 and high pressure is
created within a few seconds.
RAF 88 is a piloted hydraulic valve activated by line pressure.
The valve has two pilots, for high and 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, and remains open until the fluctuations subside.
Typical Application Recommended Flow

Nominal Diameter Flow Rate M3/h
mm Inch Max.
40 1.5 35
50 2 60
65 2.5 80
80-50-80 3-2-3 60
80-65-80 3-2.5-3 100
80 3 120
100-80-100 4-3-4 120
100 4 180
125-100-125 5-4-5 200
150-100-150 6-4-6 200
RAF 88 is located next to a booster pump to protect the supply line downstream of the pump
from water hammer damages. 150 6 400
200 8 750
Use a surge-anticipating valve to protect water lines against water hammer
damages. Uphill supply lines of considerable length and large diameter pipes are 250 10 1150
more susceptible to water hammer damages.
300 12 1700
For more info or hazard analysis of a particular network consult Raphael Engineers.
ADJ.
ADJ.
4
1
RAF 88 control mode 3 3

1
b 2
RAF Surge Anticipating hydraulic Valve VENT 2
is activated by line pressure and
MAIN LINE
controlled by two pilot valves. Both
a
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 1 2
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 RAF 88 - Surge Anticipating Hydraulic Valve
normal. The RAF is normally closed.
Only when the line pressure drops (the left one), but lower than that of the pilot but opens the right one (the high
below or rises above the preset limits, high-pressure pilot (the right one). Thus, pressure pilot) at the same time. The
the RAF 88 is piloted to open. A water ports 2 in both pilots are closed. There RAF control chamber now drains
hammer event starts with a is no flow from the main line to the through ports 2-3 of the right pilot and
considerable pressure drop, which pilots. The RAF control chamber is thus remains open. The high-pressure
cause the RAF 88 to open. Then, as connected directly to the line pressure wave is allowed to flow through. After
the water wave rolling backward, the through needle valve a. The RAF is the surges subside, and the line
valve remains open and let the pressure closed. pressure returns to normal level, both
out to diminish its impact. When line pressure drops below the pilots close and the RAF 88 follows
lower set point, the spring of the low- suit.
RAF 88- control mode pressure pilot (left) push the pilots
membrane downward and on the way
Manual: To open the RAF 88, close opens port 2, as shown in the drawing.
cocks 1,2 and 4 and open the Vent. The right pilot does not change. The Adjustment
Automatic: The RAF 88 is normally RAF control chamber drains out
closed. Ensure that all cock valves through port 2 -Vent b of the left pilot. Use needle valve a-b to control the RAF
(except the vent) are fully open. The RAF 88 opens in anticipation to a operational speed. Adjust the low and
Normally, line pressure is higher than surge. The pressure drop is soon high pilots set points by the adjusting
the set point of the low-pressure pilot followed by a surge, which closes the screws. See list of available springs
left below.
Standard RAF 88: Special Features:

Basic RAF valve Rilsan Coated Enamel coating
Self-cleaning screen filter Large capacity external filter
2 way pilot P-181 2 way high capacity pilot P-181-3/4
2 way pilot P-161B 2 way high capacity pilot P-161B-3/4
Brass needle valves -
Reinforced plastic tubing Copper or stainless steel tubing
60mm pressure gauge Glycerinated 60mm pressure gauge
Spring Selection (bar)

RAF 88
Green Blue red Yellow
Standard
2-10 0.5-4 0.5-6 2-16

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RAF

RAF 88 is adjusted to eliminate hazardous pressure surges

Typical Application Recommended Flow

RAF 88 control mode 3 3

Standard RAF 88: Special Features:

Spring Selection (bar)

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