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Relief Valve Protection
All 4000 Series models are positive displacement pumps. As the pump rotates, liquid is positively delivered to the discharge side of the
pump. If the discharge line is closed o, pressure will increase until the drive stalls and/or fails, the pump breaks or ruptures, or the
piping bursts. To prevent this from happening, the use of a pressure relief valve is required. A relief valve that directs the ow back to
the supply tank is recommended. The internal relief valve available on 4000 Series pumps is designed for overpressure protection only.
It is not intended as a ow control device or for any similar use.
Continuous operation of the relief valve will result in excessive heat buildup within the pump cavity that could cause serious internal
damage. Make certain the adjusting screw of the relief valve is located on the suction side of the pump. Tuthill species relief valve
settings based on full-bypass pressure, where 100% of the pump ow is recirculating through the valve. It is important to know that the
valve will be partially open at pressures below the full-bypass pressure. The dierence between the partially open pressure and the
full-bypass pressure is dependent on pump speed and uid viscosity. If an internal relief valve has not been supplied with the pump
some other means of protection must be utilized. These include in-line safety relief valves, pressure shutdown switches or other similar
devices.
4100 Series
Unless otherwise specied at the time of order, all 4100/4120 pumps are supplied with the standard spring, with a range of 55-120 PSI
(4 to 8 bar), set to relieve at 55 PSI (4 bar) full-bypass on 200 SSU oil. The standard spring range in the 4108 is 40-70 PSI (3 to 5 bar)
and is set to relieve at 55 PSI. The relief valve setting should be reset in the actual operating condition. To adjust the relief setting within
the range of a given spring’s capability
• Remove the acorn nut (Not supplied with models 4108)
• Insert a screwdriver into the slot of the adjusting screw and hold it steady
• Loosen the locking nut with a wrench by turning counterclockwise
• Throttle the outlet line until the dierential pressure at the pump port reaches the desired level
• If the pressure fails to reach this level with the throttling valve closed, turn the adjusting screw inward (clockwise) to
increase to desired pressure
• If the pressure reaches the desired level before the throttling valve is completely closed, turn the adjusting screw outward
(counter clockwise) to lower to the desired pressure
• Retighten the nut to lock the setting in place and replace the acorn nut (if supplied)
• Recheck the pressure gauge reading
CAUTION
If the adjusting screw is backed out (counter clockwise) too far, the spring and poppet could fall into pump.
4300 Series
Unless otherwise specied at the time of order, all 4310 pumps with an internal relief valve are supplied with the standard spring, with
a range of 30-225 psi (10 - 200 psi in size 2 pumps), set to provide full bypass relief at 90 psi. To adjust the relief setting within the range
of a given spring’s capability.
With a small wrench, hold the adjusting screw steady then with a second wrench, loosen the locking nut by rotating counterclockwise.
Throttle the outlet line until the dierential pressure at the pump port reaches the desired level. If the pressure fails to reach this
level with the throttling valve closed, turn the adjusting screw inward (clockwise) until the desired pressure is reached. If the pressure
reaches the desired level before the throttling valve is completely closed, turn the adjusting screw outward (counterclockwise) until the
desired pressure is reached. Retighten the nut to lock the setting in place and recheck the pressure gauge reading
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