Inlet pressure

Inlet pressure, or pump intake pressure, describes the pressure available where the suction pipe meets the booster pump. The inlet pressure derives from the pressure of the water supplier or the water pressure created if the booster draws from a break tank. The inlet pressure can be negative or positive; however, negative inlet pressure normally occurs when the booster has to suck water from tanks which are placed below the booster. 

The inlet pressure is used for calculating the required boost from the booster pumps as well as the NPSHa (Net Positive Suction Head available). NPSHa is used for determining if a certain pump can be used in a certain application and how the suction pipe is sized. 

The required boost from the boosting set can be calculated as follows: 

Pset = Ptap(min) + Pf + (hmax/10.2) 

Pset = the required outlet pressure from the booster 

Ptap(min) = the required minimum pressure at the highest tapping point in the zone 

Pf = pipe pressure loss from the booster outlet to the highest tapping point 

hmax = the height from the booster to the highest tapping point 

Pboost = Pset - Pin(min)  

Pboost = the required boost from the pressure boosting set 

Pset = the required outlet pressure from the booster (calculated above) 

Pin(min) = the inlet pressure to the booster 

Whether the inlet pressure is negative or positive influences the optimum placement of the non-return valve. When the inlet pressure is negative, the non-return valve should be placed before the pump, so that the water does not drain from the pump during standstill. When the inlet pressure is positive, the valve can be placed after the pumps, ensuring that the high pressure from the booster doesn’t spread to the mains. 

Legend 

1) Pset = the required outlet pressure from the booster 

2) Ptap(min) = the required minimum pressure at the highest tapping point in the zone 

3) Pf = pipe pressure loss from the booster outlet to the highest tapping point 

4) hmax = the height from the booster to the highest tapping point 

5) Pboost = the required boost from the pressure boosting set 

6) Pset = the required outlet pressure from the booster (calculated above) 

7) Pin(min) = the inlet pressure to the booster 

The Grundfos range of booster sets meets the requirements for pressure boosting applications. Use the Grundfos sizing tool to calculate the boost required from the available pump intake pressure.