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The Performance Curve and Energy Loss of Sand Pump

Posted by:    Time:2014-02-21     click:

Performance curve of sand pump is the relationship curve between the basic performance parameters of centrifugal pumps (flow, head, power and efficiency) at a certain rotating speed. For the performance curve is measured at a fixed speed, so it only apply appropriate for that speed. That is why characteristic curve is indicated with the numerical of the speed. There are three curves painted on performance curves (now two): H-Q curve; N-Q curve.

A. H-Q curve

Trend: head of sand pump is decreasing with the increase of flow in a large flow range. Different models centrifugal pump have different shape of H-Q curve. Relatively flat curve is suitable for occasions of little change in pressure head and large flow changes; while a steep curve is suitable in the occasions of large change in pressure head and not allowable large changing in flow.

B. N-Q curve

Trend: N-Q curve represents the relationship between flow Q and shaft power N, and N increases with Q increasing. Apparently, when Q is zero, the power consumption N of the pump will be the minimum. To reduce the starting power, when start centrifugal pump the outlet valve should be closed.

Energy loss of Horizontal single-stage centrifugal sand pump

In fact, in the processing of liquid flowing from the pump body to the pump outlet, there are three kinds of energy loss, which decrease the efficiency of the centrifugal pump.

One, the hydraulic loss

There will always be friction energy loss when liquid flow through channel and contact the surface, that energy loss mainly depends on the channel length, size, shape, surface roughness and the liquid flow rate characteristic. It includes the shock loss produced when liquid flow into the blade and flow through the liquid pressure room; The resistance loss of fluid flowing through the suction chamber and the diffuser pipe friction along the way and liquid flows through the vortex loss caused by turning around and contraction or expansion.

Two, the volume loss

Leakage caused by the loss of seal gap called volume loss. The volume loss includes seal ring leakage loss, balance mechanism between the drain f loss, leakage loss and packing leakage loss. In order to reduce volume loss, increase seal clearance narrow as far as possible and improve the seal wear, assembly accuracy.

1. Seal ring leakage loss

When the sand pump works, there is a pressure difference on both sides of the sealing ring, so there will always be a part of the liquid from the exit impeller leakage to inner impeller. All the Leakage liquid energy is used to overcome the resistance of the sealing ring.

2. Leakage loss of balance mechanism

In the vertical multistage pump, with the balance axial thrust mechanism, such as balance hole, pipe, balance disc etc. Because there is pressure difference on both side of the balance mechanism, a part of the liquid leakage go from the high pressure region to the low pressure area.

3. Inter stage leakage loss

In volute pump, inter stage pressure on both sides of partition is unequal, and thus there is leakage loss.

4. Mechanical loss

Mechanical loss includes the friction loss between the cover and the outer surface of the liquid, and friction loss of sand pump shaft, the bearing, sealing device and impeller (wheel resistance loss). Mechanical loss and flow are independent.

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