Graco C Series Instructions And Parts List page 2

Pressure Relief Procedure.
WARNING
PRESSURIZED EQUIPMENT HAZARD
The system pressure must be manually relieved to
prevent the system from starting or spraying accidentally.
To reduce the risk of an injury from accidental spray from
the gun, splashing fluid, or moving parts, follow the
Pressure Relief Procedure whenever you:
D are instructed to relieve the pressure,
D stop spraying,
D check or service any of the system equipment,
D or install or clean the spray nozzle.
1. Shut off the power to the pump. If you are using an air–
powered pump, open the bleed–type master air valve.
2. Trigger the gun.
3. Relieve the line pressure by turning the adjusting screw
(26) counterclockwise until there is no spring pressure.
Installation
This valve is used in a circulating system to regulate the back
pressure to spray guns and to maintain the proper circulating
pressure throughout the system.
The valve is adjustable to control fluid pressure in a circulat-
ing system from 0 to 180 psi (0 to 12.4 bar, 0 to 1.24 MPa).
CAUTION
To prevent damage to the diaphragm, the hard carbide seat
and stem, and other sensitive parts, handle the valve care-
fully.
Install the valve in the return line of the spray guns, down-
stream from the last gun. See Fig. 1. Connect the return line
to the 3/8 npsm(m) inlet (22) and the 3/8 npsm(f) outlet (11).
Be sure the connections match the direction of fluid flow in
the line. See Fig. 2.
B
A
Fig. 1
2 306640
Fig. 2
The back–pressure valve controls pressure in the fluid
return–line. Adjust the pump pressure and the back–pressure
valve for the best combination of spraying pressure and fluid
circulation.
To adjust the back–pressure valve, loosen the locknut (27)
and insert the hex key wrench (7) into the socket on the
adjusting screw (26). Turn the screw clockwise to increase
pressure in the return line. Turn the screw counterclockwise
to decrease pressure in the return line. Lock in the adjust-
ment by tightening the locknut (27).
NOTE: Always check and adjust the back pressure valve if
you make changes to the system such as a change of fluids,
the length of the lines, and the number of spray guns.
Flush the valve with a compatible solvent whenever the rest
of the system is being flushed. Fully open the valve before
flushing by turning the adjustment screw counterclockwise.
Always use the lowest possible pressure when flushing.
NOTE: Clean and check the valve regularly to maintain it in
good working condition. Refer to the Parts drawing on page
3.
1. Remove the valve from the system.
C
2. Disassemble the pressure gauge (5) and the tube (16)
from the inlet adapter (22). Remove the inlet adapter and
the outlet union (11) from the housing (25).
3. Unscrew the cap (28) from the housing (25). Remove the
D
adjusting screw (26) and the locknut (27).
4. Remove the spring plate (15) and the spring (13).
E
5. Loosen the cap nut (4). Disassemble the diaphragm and
its related parts (2,10, 18, 19, 20, 21).
F
Be careful not to damage the valve seat (1) or stem (2)
04521 which are made of hard carbide.
22
Operation
Service
CAUTION
11
04520