If reverse spin is possible, a four-quadrant curve representation can be selected based on your pump’s specific speed. According to affinity laws, impellers with similar geometry and streamlines tends to have similar specific speeds.

To simulate a pump for which no pump curve is available or whenever there is a possibility of reverse flow or spin, selecting the built-in four-quadrant curve corresponding to the correct pump type is essential. Despite some approximation, HAMMER CONNECT will output physically meaningful results provided you select the correct four-quadrant curve based on your pump’s specific speed. The results can help you decide whether or not additional detail is critical or even required.

To select an appropriate four-quadrant pump curve in HAMMER CONNECT, simply calculate the specific speed and select the closest available setting in the Specific Speed field of the pump’s Element Editor. You can calculate your pump’s specific speed, N_s, using the following equation:

Where:

N_s is specific speed (rpm)

N is pump rotational speed (rpm)

Q is flow rate (m³/s or gpm) at te point of best efficiency

H is total head (m or ft) per stage at the point of best efficiency

“Table 4-3: Specific Speeds for Typical Pump Categories in both Unit Systems” shows typical values of specific speed for which an exact four-quadrant representation is built into HAMMER CONNECT. Centrifugal pumps tend to have lower specific speeds than axial-flow or multi-stage pumps. Few four-quadrant characteristic curves are available because they require painstaking laboratory work.

The results of hydraulic transient simulations are not as sensitive to the specific speed selected, provided that a check valve is installed. You do not need to add a check valve because every pump in HAMMER CONNECT has a built-in check valve immediately downstream of the pump.

Specific Speeds for Typical Pump Categories in both Unit Systems