Sun Pumps SJT10-120BL - Manual (Page 7)

Figure 2 Typical Shallow Well Pump Installation
3.4 Adjusting The Pressure On The Jet Pump (For Open Discharge)
If the system is used with an open discharge, pumping into a non-pressurized tank, there must be internal pressure in the pump housing for the
jet to operate properly. This is provided by adjusting the control valve on the discharge pipe as shown in Figure 2. (Not included with the
pump.)
The required minimum pressure varies with pump speed, elevation and suction lift so there is no easy way of predetermining the minimum
internal operating pressure. With solar power and changing sunlight conditions there will be varying motor speeds so the best time to make
the adjustment is at mid-day in with clear skies with full sunlight.
The easiest way to adjust the control valve is by sound. If the internal pump pressure for your specific pumping application is too low the
pump will cavitate and cavitation makes an audible sound. Cavitation occurs when the local static pressure is below the vapor pressure. To
stop the pump from cavitating, the internal pump pressure must be increased above the vapor point. To do this the control valve on the
discharge pipe is slowly adjusted toward the closed position until you hear the cavitation stop. You can watch the pressure gauge to see what
this minimum internal pressure is for your application.
3.5 Typical Pressure System Installation
1. Follow the same installation procedures in Section 3.3 for the “Shallow Well Pump Installation” with the exception of the location of
the pressure gauge and the control or gate valve.
2. Install a check valve control center, a pressure gauge and a pressure switch between pump and the pressure tank. Make sure both the
pressure gauge and the pressure switch are on the tank side of the check valve in the 1/4” NPT tapped holes.
3. Install a gate valve on the discharge pipe as shown in Figure 3.
4. When choosing a pressure switch make sure the “minimum pressure” required by the jet is at or above the cut-in pressure on the
pressure switch. Usually a 30-50 pressure switch is a safe choice if you do not know what it is. Keep in mind the cut-in pressure can
be adjusted up or down to fit your specific application.