FAQs

Pump Talk

HEAD

Centrifugal pump curves show ‘pressure’ as head, which is the equivalent height of water with S.G. = 1.

This makes allowance for specific gravity variations in the pressure to head conversion to cater for higher power requirements. Positive Displacement pumps use pressure (i.e. psi or kPa) and then multiply power requirements by the S.G.

STATIC HEAD

The vertical height difference from surface of water source to centreline of impeller is termed as static suction head or suction lift (‘suction lift’ can also mean total suction head).

The vertical height difference from centreline of impeller to discharge point is termed as discharge static head.

The vertical height difference from surface of water source to discharge point is termed as total static head.

TOTAL HEAD / TOTAL DYNAMIC HEAD

Total height difference (total static head) plus friction losses & ‘demand’ pressure from nozzles etc. i.e. Total Suction Head plus Total Discharge Head = Total Dynamic Head.

NPSH

Nett positive suction head — related to how much suction lift a pump can achieve by creating a partial vacuum. Atmospheric pressure then pushes liquid into pump. A method of calculating if the pump will work or not. (more)

S.G.

Specific gravity. Weight of liquid in comparison to water at approx 20 deg c (SG = 1).

SPECIFIC SPEED

A number which is the function of pump flow, head, efficiency etc. Not used in day-to-day pump selection, but very useful as pumps with similar specific speed will have similar shaped curves, similar efficiency / NPSH / solids handling characteristics.

VAPOUR PRESSURE

If the vapour pressure of a liquid is greater than the surrounding air pressure, the liquid will boil.

VISCOSITY

A measure of a liquid’s resistance to flow. For example, how thick it is. The viscosity determines the type of pump used, the speed it can run at, and with gear pumps, the internal clearances required.

FRICTION LOSS

The amount of pressure / head required to ‘force’ liquid through pipe and fittings.

PSI

The pound per square inch or, more accurately, pound-force per square inch (symbol: psi or lbf/in2 or lbf/in2 or lbf/sq in or lbf/sq in) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to an area of one square inch:

1 psi approximately equals 6,894.757 Pa, where pascal (Pa) is the SI unit of pressure

KPA

The pascal (symbol: Pa) is the SI derived unit of pressure, It is a measure of force per unit area, defined as one newton per square metre. In everyday life, the pascal is perhaps best known from meteorological barometric pressure reports, where it occurs in the form of hectopascals (1 hPa ≡ 100 Pa) or kilopascals (1 kPa ≡ 1000 Pa).[1] In other contexts, the kilopascal is commonly used, for example on bicycle tire labels.[2] One hectopascal corresponds to about 0.1% and one kilopascal to about 1% of atmospheric pressure (near sea level). One hectopascal is equivalent to one millibar; one standard atmosphere is exactly equal to 1013.25 hPa.

Centrifugal pump.

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits into the downstream piping system.[1][2] Centrifugal pumps are used for large discharge through smaller heads.

Centrifugal pumps can further be classified as

• end suction pumps
• in-line pumps
• double suction pumps
• vertical multistage pumps
• horizontal multistage pumps
• submersible pumps
• self-priming pumps
• axial-flow pumps
• regenerative pumps

Positive Displacement Pumps

The positive displacement pump operates by alternating of filling a cavity and then displacing a given volume of liquid. The positive displacement pump delivers a constant volume of liquid for each cycle against varying discharge pressure or head.

The positive displacement pump can be classified as:

• Reciprocating pumps — piston, plunger and diaphragm
• Power pumps
• Steam pumps
• Rotary pumps — gear, lobe, screw, vane, regenerative (peripheral) and progressive cavity

Submersible Pumps

A submersible pump (or electric submersible pump (ESP)) is a device which has a hermetically sealed motor close-coupled to the pump body. The whole assembly is submerged in the fluid to be pumped. The main advantage of this type of pump is that it prevents pump cavitation, a problem associated with a high elevation difference between pump and the fluid surface. Submersible pumps push water to the surface as opposed to jet pumps having to pull water. Submersibles are more efficient than jet pumps. Get more information from our online pump shop.

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