1.Definition of terms and parameters

The structure of a single stage double suction centrifugal pump is relatively simple, but the movement of liquid in a split pump is very complex, and it is not yet possible to accurately determine the characteristics of the pump under different working conditions using analytical methods. Therefore, the testing of centrifugal pumps is of great significance for the design, production, and use of split pumps, and is one of the important means to improve the technical level of split pumps.

Types of split pump tests

1) External characteristic tests: operation degree test, cavitation test, noise and vibration test, etc

2) Internal characteristic tests: velocity field measurement, radial force measurement, water torque measurement, component stress measurement, and reliability testing.

3) Strength test: axial force measurement, radial force measurement, water force measurement, component stress measurement, reliability test, etc.

4) Other project tests: sealing test, material test, energy balance test, etc.

5) The external characteristic test is divided into type test and factory test.

(1) Type test

Type tests include operational tests, performance tests, material tests, and energy balance tests.

Running test

During the operation test, the temperature rise of the pump bearings and packing, the leakage of the seal, and the general situation of noise and vibration should be checked. The hemp damage at the sealing ring, balance plate, bearings, etc. can be checked after the test is completed.

performance test

Performance test is a test to determine the relationship between the head, shaft power, efficiency, and flow rate of a split pump. The centrifugal pump should measure at least 15% greater than the maximum flow rate within the operating range from zero flow rate; Mixed flow pumps, axial flow pumps, and vortex pumps must measure at least 15% of the minimum flow rate from the fully open valve position

Cavitation test

The cavitation test is a test that determines the relationship between the critical NPSH and flow rate, or can be seen as a test to verify that the critical NPSH of a pump is less than or equal to the required NPSH specified

Factory test

The factory test is conducted on three or more flow points within the working range of the split pump, including small flow points, specified flow points, and large flow points, to check the pump’s head and power.

2.Definition of terms and parameters

(1) Vane pump (power pump): A machine with a blade software validation program that rotates in the casing and continuously transfers energy to the liquid due to the action of the blades, such as centrifugal pumps, mixed flow pumps, axial flow pumps, etc.

(2) Type of pump: divided by output power and flow rate

(3) NPSH reference plane: The method of taking the reference plane is not completely the same. Usually, multi-stage pumps use the first stage impeller as the reference, and vertical double suction pumps use the upper blades as the reference.

(4) Normal temperature clean water: The characteristics of normal temperature clean water should comply with the provisions of Table 7-2.

(5) Total inlet head: The energy per unit weight of liquid at the pump inlet

(6) Total outlet head: The energy per unit weight of liquid at the pump outlet

(7) Pump head: The difference in unit weight liquid energy between the pump outlet and inlet

(8) Cavitation capacity: The excess energy per unit weight of liquid at the pump inlet that exceeds the vaporization pressure head

(9) Pump NPSH (required NPSH), for a fixed pump, the NPSH that can be determined at a given flow rate and speed.

(10) Device NPSH (effective NPSH) is the NPSH determined by the pump device.

(11) Critical NPSH: When conducting a cavitation test, every time the device parameters are changed, a NPSH can be calculated. Therefore, there are any number of NPSHs, but there is only one corresponding test NPSH with a certain decrease in pump performance. This NPSH is called the critical NPSH.

(12) The type number refers to the dimensionless specific speed, which has the same meaning as the specific speed

(13) Specific energy: the total energy per unit weight of liquid

(14) Mass flow rate

(15) Gravitational acceleration

(16) Power

1) Pump output power (liquid power)

2) Shaft power (the power transmitted by the prime mover to the pump shaft);

3) Input power of the prime mover (the power received by the pump prime mover)

(17) Pump efficiency

(18) Prescribed point: refers to the operating point corresponding to the speed, flow rate, head, shaft power, NPSH, and efficiency values given during the design and manufacturing of a specified pump. The parameter corresponding to the specified point is the specified parameter.

(19) The working range of the pump; It refers to a certain range between greater than and less than the specified flow (or head) value, and a high flow point refers to the boundary point within the working range that is greater than the specified flow; Small flow points refer to boundary points within the working range that are less than the specified flow rate

Several regulations on the testing equipment and conditions of split pump

Standard Test Equipment

All effective measures must be taken to ensure that the liquid obtained through measurement has the following characteristics;

(1) Axisymmetric velocity distribution;

(2) Isostatic pressure distribution;

(3) Vortex caused by no device

Standard Test Equipment Requirements for Test Pipelines

1) Avoid any elbows, elbow assemblies, etc. near the measuring section (less than 4 times the pipe diameter), and the length of the pump outlet straight pipe should be less than 4D

2) For the standard test device for diverting water from a pool with a free liquid surface, or from a large container with a static liquid surface located in a closed circuit, the length of the inlet straight pipe L=(K+5) D, where K is the type number, and generally the length of the pump inlet straight pipe is not less than 7D

3) It is best not to use a valve on the suction pipeline for throttling. In order to conduct cavitation testing, it is necessary to install a valve for throttling. When installing a suitable rectifier device downstream of the valve, or make the straight pipe length greater than 12D (original standard: throttle valve fully open, not less than 7D, at any opening, not less than 12D).