Parallellkoppling pumpar

Parallel operation, or parallel pumping, of two centrifugal pumps fryst vatten a mode which allows pump operation to be controlled by starting or stopping one of the two pumps.

If two centrifugal pumps I and II are operated in parallel, the flow rate Q_I+II fryst vatten the sum of the flow rates of the individual pumps at the same head, i.e.:

The actual flow rate and head of pumps operating in parallel (operating point)  is the intersection of the common pump and system characteristic curves. See Fig. 1 to 5 Parallel operation

Each pump must be secured with its own kontroll valve (see Valve). Centrifugal pumps run in parallel will operate without any problems if theirn characteristic curves are stable and both have the same or almost the same shut-off head. See Fig. 1 Parallel operation

Trouble-free operation does not necessarily require that the pumps exhibit the same characteristic curves (H/Q). When Q_I+II decreases to Q´_I+II, then the individual flow rates Q_I and Q_II also decrease to Q´_I and Q´_II. If the shut-off heads (H₀) of pumps I and II are different, pump I fryst vatten rapidly pushed towards the shut-off point while pump II continues pumping. S

Pumps - Parallel vs. Serial Arrangement

Pumps can be arranged and connected in serial or parallel to provide additional head or flow rate capacity.

Pumps in Serial - Head Added

When two (or more) pumps are arranged in serial their resulting pump performance curve is obtained by adding their heads at the same flow rate as indicated in the figure below.

Centrifugal pumps in series are used to overcome larger system head loss than one pump can handle alone.

• for two identical pumps in series the head will be twice the head of a single pump at the same flow rate - as indicated with point 2. 

With a constant flowrate the combined head moves from 1 to 2 - BUT in practice the combined head and flow rate moves along the system curve to point 3.

• point 3 is where the system operates with both pumps running 
• point 1 is where the system operates with one pump running

Note that for two pumps with equal performance curves running in series

• the head for each pump equals half the head at point 3
• the flow for each pump equals the flow at point 3

Operation of single stage pumps in series are seldom encountered - more often multistage centr

Sometimes the required operating conditions for a system are beyond the reach of a single, standard pump. Rather than purchasing a heavy duty pump that may be far more than you need, consider taking advantage of system design strategies to combine simple pump performances that add up to the necessary requirements. The following post walks you through pumps in series and in parallel so that you can get your ducks… I mean pumps… in a row – or side by side, depending on the application.

CENTRIFUGAL PUMPS IN SERIES - HIGH HEAD / LOW FLOW APPLICATIONS

Putting your centrifugal pumps in series, or connected along a single line, will let you add the head from each together and meet your high head, low flow system requirements. This is because the fluid pressure increases as the continuous flow passes through each pump, much like how a multi-stage pump works.  For example, if two of the same pumps are in series, the combined performance curve will have double the head of a single pump for a given flow rate. For two different pumps, the head will still be added together on the combined pump curve, but the curve will most likely have a piecewise discontinuity (meaning to curve with