1. Differential head

  2. Differential pressure

  3. UK / USA Gallons

  4. 316L / 316 / 304

  5. Pump performance curves


Differential head

We cannot tell you what discharge head a pump will provide unless you tell us the suction head (the head at the pump inlet). Think of a pump as ‘adding’ head to your system. For example, imagine a pump that ‘adds’ 20m head. If the head at the pump inlet is 5m then the discharge head will be 25m.
The amount of head that the pump ‘adds’ to the system is called the ‘differential head’. So, what we need to know is not what discharge head you require, but how much head would you like the pump to add to your system.












Differential pressure

Differential Pressure = Discharge Pressure – Suction Pressure

If you give us pressure figures, we calculate the corresponding head figures for you, provided that you let us know the density (specific gravity) of the liquid (see section 6).














UK / USA Gallons

UK Gallons

1 UK gallon = 4.5461 litres (dm³)
1 m³ = 219.97 UK gallons

Approximately 1 m³ = 220 UK gallons

USA Gallons

1 USA gallon (231 cubic inches) = 3.7854 litres (dm³)
1 m³ = 264.17 USA gallons

Approximately 1 UK gallon = 1.2 USA gallons










316L / 316 / 304


Country Standard



United Kingdom BS 1449 Part 2 1975
BS 970 Part 4 1970
France AFNOR   Z2CND17-12
Germany Deutsche Stoff No. 1.4404
Italy U.N.I.  X2CrNiMo1713
Japan J.I.S SUS 33
Sweden S.I.S 2353


United Kingdom BS 1449 Part 2 1975
BS 970 Part 4 1970
France AFNOR   Z6CND17-11
Germany Deutsche Stoff No. 1.4401
Italy U.N.I.  X5CrNiMo1713
Japan J.I.S SUS 32
Sweden S.I.S 2343


United Kingdom BS 1449 Part 2 1975
BS 970 Part 4 1970
France AFNOR   Z6CN18-09
Germany Deutsche Stoff No. 1.4301
Italy U.N.I.  X5CrNi1810
Japan J.I.S SUS 27
Sweden S.I.S 2332







Pump performance curves


Pump performance curves supplied will show differential head (in metres) against flow (in m³/h) and will be based on tests pumping water at 20°C using a 50Hz supply. They therefore reflect the majority of products (eg milk, beer, wine, spirits, caustic solutions for CIP, dilute acids, etc).

Density affects the differential pressure (but not the head) and power. For a specific gravity of 1.3, the differential pressure and the power required will be 1.3 times the corresponding values when pumping water.

Viscosity affects flow, differential head, efficiency and power. For liquids with a different viscosity to water (1 cP), corrections must be made. Please contact MDM Pumps Ltd for advice.

For an existing pump

To provide you with a performance curve for an existing pump manufactured by MDM Pumps Ltd, we need to know the pump serial number.

For a new pump

If you wish to see a pump performance curve for a new pump that you require, you will of course need to provide us with all the essential information for a quotation. Please note that prior to the testing of a pump, we can only provide guideline performance curves.

Non-standard curves

We do provide non-standard pump performance curves on request; eg for a 60Hz supply or if pumping a viscous liquid.