Spec Sheet

Ref 300981 Rev. B
10-18
GENERAL PUMP 1174 Northland Drive • Mendota Heights, MN 55120
Phone: [phone] • Fax: [phone] • e-mail: [e-mail] • www.generalpump.com
YVB4021HT
GENERAL PUMP A member of the Interpump Group
PROBLEMS PROBABLE CAUSES SOLUTIONS
Frequent Unloader Cycles Damaged check valve o-ring
Leaking connections
Restricted bypass
Replace
Check and renew
Clean or adapt
Unloader does not come up to
pressure
Unloader not properly sized
Piston O-rings worn out
Debris between seat and shutter
Worn nozzle
Change spring or type of valve
Replace
Clean the seat
Replace
Excessive pressure spikes There is not a minimum of 5% flow in bypass
Excessive flow in bypass
Spring totally compressed
Reset
Change type of valve ar adjust passages
Loosen knob and change nozzle
Unloader does not bypass
at low pressure
Jammed check valve
Check valve O-ring worn
Debris in check valve
Clean or replace
Replace
Clean
TROUBLESHOOTING
MAINTENANCE
Maintenance must be carried out by Qualified Technicians.
STANDARD: Every 400 working hours (10,000 cycles), check and lubricate the seals with water resistant grease.
SPECIAL: Every 800 working hours (20,000 cycles), check the wear of the seals and internal parts and, if necessary,
replace with original General Pump parts taking care during installation and to lubricate with water resistant grease.
The manufacturer is not responsible for damage as a result of incorrect fitting and maintenance.
INSTRUCTIONS (cont.)
DISCHARGE SYSTEM AND WATER ADDUCTION
We recommend to fit the valve with the bypass discharge returned to a tank. It is advisable that the tank be fitted with baffles to
reduce eventual turbulence and air bubbles generated by the emission of the bypass flow which could be harmful for the pump. With
elevated flow or near to the maximum flow of the valve, the installation with a recirculation of bypass direct to the pump could cause
potential pressure spikes harmful to the pump.
PRESSURE ADJUSTMENT/CALIBRATION
The desired working pressure must be adjusted with the system running and the gun opened. Adjust the pressure by screwing or
unscrewing the adjustment screw/knob. The operation is easier if the correct nozzle has been chosen (see paragraph “installation”).
When screwing the screw/knob a consequent pressure increase must be matched. If, before reaching the desired pressure, there is
no pressure increase when screwing the screw/knob, do not force but check the correct ration nozzle/flow rate - pressure and, if
necessary, fit a nozzle with a smaller size.
Pressure Trapping Unloader