# What Is Discharge Pressure?

M. McGee

Discharge pressure describes the pressure of a liquid as it leaves a pump. Higher discharge pressures equal greater force behind the release while lower pressure means less. A pump’s discharge pressure is influenced, but not determined, by other aspects of the pump. While this term is independent of other descriptions for a pump, the overall combination of flow rate, suction pressure and capacity will determine the total power of the system.

A pump’s discharge pressure is actually the last step of the system. Most pumps begin with suction, or suction pressure. This describes how much liquid the pump can pull in at any given time. Since most pumps are designed for circumstances with plenty of material to move, this part of the system is often not much of a factor. The only common place where it comes into usefulness is when the pump needs to pull material against gravity or another basic force.

The next main part of a pumping system is flow rate. This factor describes how much material can flow through the pump at any given moment. The flow rate is directly influenced by how much material comes in, suction, and how much material goes out, discharge. The flow rate can describe the amount of material that will move over longer periods, where the other factors are generally more immediate.

Capacity is a measurement of how much liquid the pump can hold at a time. In some pumps, this is simply the amount from the input to output of the system. Other types of pumps will essentially store material within the system to create additional pressure and improve discharge.

The final step in a pump system is discharge pressure. This pressure is influenced by the amount of material in the system; if the system is low on material, the pressure will likely be lower, but the majority of the value is independent. A pump’s discharge pressure is generally determined by two main factors: pump strength and nozzle design. The strength of the motor within the pump determines the strength — stronger motors create higher pressures. The shape of the nozzle is the final factor; narrow and constricted nozzles create higher pressure than wide or open ones.

It is common to describe discharge pressure in terms of vertical feet. This means that if the pump were operating under optimal conditions, the output would shoot straight up for a set number of feet; the higher the discharge pressure, the greater the number. The also makes it simple to determine the pressure at other angles; for instance, it is increased by 50 percent when on its side and 100 percent when pointing down.