Created on 12/23/2015
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2015 Sun Hydraulics Corporation See www.sunhydraulics.com for detailed product information 1 of 2
MODEL
QCDB
20%, accumulator sense, pump unload valve with check - pilot capacity
SERIES 1 / CAPACITY: 60 L/min. / CAVITY: T-21A
The accumulator sense, pump unload pilot valve is used to sense pressure in an accumulator at port 2 of the valve
and when the pressure at port 2 reaches the valve setting, port 3 connects to port 4 to vent a relief valve and
unload the pump. This valve has a 20% ratio between unload setting and reset; when pressure at port 2 falls below
80% of the valve setting, port 3 is blocked from port 4 and the pump will come back online to recharge the
accumulator.
The integral free-flow check valve is suitable for pump flows up to 15 gpm (60 L/min). For higher capacity pumps,
another version of accumulator sense, pump unload cartridge, QPAB, which requires a separate check cartridge is
available.
TECHNICAL DATA
Maximum Operating Pressure 350 bar
Check Cracking Pressure 0,3 bar
Pressure Drop, Port 1 to Port 2 7 bar@60 L/min.
Pilot Flow Capacity 0,75 L/min.
Adjustment - Number of Clockwise Turns to Increase Setting 5
Locknut Hex Size 15 mm
Locknut Torque 9 - 10 Nm
Seal kit - Cartridge Buna: 990-021-007
Seal kit - Cartridge Polyurethane: 990-021-002
Seal kit - Cartridge Viton: 990-021-006
(L)CONTROL
L Standard Screw Adjustment
C Tamper Resistant - Factory Set
(A)ADJUSTMENT RANGE
A 1000 - 3000 psi (70 - 210 bar), 1000 psi
(70 bar) Standard Setting
B 500 - 1500 psi (35 - 105 bar), 500 psi
(35 bar) Standard Setting
C 2000 - 5000 psi (140 - 350 bar), 2000
psi (140 bar) Standard Setting
D 250 - 800 psi (18 - 55 bar), 250 psi (18
bar) Standard Setting
(N)SEAL MATERIAL
N Buna-N
V Viton
MATERIAL/COATING
Standard Material/Coating
/AP Stainless Steel, Passivated
/LH Mild Steel, Zinc-Nickel
snhy.com/
QCDB
TECHNICAL FEATURES
The pressure differential between unload and reset will be within +/- 1% of the stated ratio of the valve with up to an additional 25 psi (1,7 bar) due to dynamic seal
Model Code Example: QCDBLANCONFIGURATION OPTIONS
Created on 12/23/2015
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2015 Sun Hydraulics Corporation See www.sunhydraulics.com for detailed product information 2 of 2
friction.
The accumulator sensing area is positively sealed.
The spool design of this valve allows it to maintain a fixed differential ratio because the areas are created by diameters on the spool that will not wear or change
with use.
Minimum clearances between the spool and sleeve and a seal on the pilot piston diameter significantly reduce the potential for silting.
When applying this cartridge, a separate drain line is required to prevent erratic operation caused by tank line pressure fluctuations.
NOTE: Careful consideration should be given when selecting an adjustment range. System pressure drops and flows tend to affect the operation of unloading
valves. Low operating pressures combined with low differentials result in a very narrow band between unload and reset, requiring precise system design. High flow
rates typically mean high pressure drops, which subtract from the differential the valve has to work with.
Sun has designed a variety of standard accumulator/pump unload assemblies with a variety of features. These assemblies can be found on our website under
SOLUTIONS: ACCUMLATOR SENSE, PUMP UNLOAD.
Incorporates the Sun floating style construction to minimize the possibility of internal parts binding due to excessive installation torque and/or cavity/cartridge
machining variations.
PERFORMANCE CURVES
