China piping solution supplier: www.epowermetals.com

Three stages and 10 links of centrifugal pump operation

The management of pump stability in the process industry can be divided into three stages.

  • 1) pump selection and stability determination prior to installation.
  • 2) Preparation for start-up.
  • 3) Ensuring stability after start-up.

Centrifugal pumps need to do their homework in the following 10 areas in order to operate more effectively and stably.

Selection of pump

As long as the centrifugal pump in close to the design conditions of operation, generally can achieve good performance and maintenance time interval. But it should be noted that the “design” refers not only to the pressure, flow, temperature and other process parameters, but also includes the pressure and movement of the flange, coupling pressure and movement, bearing lubrication and similar mechanical factors. The design of the old set of pumps can only operate in the non-design conditions for a short period of time, and then the pump performance level will decline. Therefore, you should choose a pump that operates near the maximum efficiency point (BEP).
Centrifugal pumps with high suction specific speed can usually only achieve good operation in a narrow range. Backflow occurs in high head pumps that attempt to use large impeller inlets to reduce NPSHR.
Pumps with low NPSHR have a suction specific velocity of around 12,000. If the normal flow rate deviates from the BEP flow rate, internal backflow can occur, which makes the pump less stable in operation. Turbulence can cause corrosion of the impeller and mechanical seal action, bearing loads and shaft deflection. The expected service life of centrifugal pump components can be affected by many factors, including pump suction specific speed, flow percentage (Q actual/QBEP), NPSH margin (NPSHA-NPSHR), head rise at each stage and pump casing design. User demand for high efficiency, low cost and low NPSHR pumps drives the suction specific speed to 12,000 or more, when the actual flow rate has a small offset relative to the BEP flow rate. The ideal suction ratio speed of the pump should be around 8,500.

The choice of seal

Packing seals have retired from the historical stage, mechanical seals and dry gas seals have been used in large numbers, commonly used for mechanical seals, mechanical seal products and technology itself is very mature, the material of the seal end face must be able to quickly transfer the heat generated to prevent fluid evaporation. Silicon carbide with its high thermal conductivity and high hardness has become the first choice of seal face material. The flushing scheme of the seal needs to be carefully considered in pump selection.

Pipe mouth pressure

When the flange of the pipe and the pump casing are bolted together, the external pressure caused by the weight of the pipe, thermal expansion and the weight of the process fluid will all exert pressure on the pump. These pressures will cause the pump casing to deform, causing internal deflection, resulting in friction between the pump casing, impeller and shaft, and even shaft stalling. They will create moments around the pump that will cause deflections between the pump and the drive shaft, leading to premature failure of couplings, bearings or mechanical seals. Therefore, limits must be set for the pressure and torque at these orifices. For the piping designer, these limits are the maximum pressure values that can be applied to the pump by the piping.

Storage

After the pump has been properly designed and someone has ordered it, the seller will deliver the pump to the buyer and wait for installation. All pumps are wrapped in a waterproof tarpaulin, making sure the tarpaulin completely covers the top and bottom of the pump to prevent the bearings and couplings from getting dusty. Place the pump in a rainproof and dustproof place to avoid dust accumulation and moisture.

Position of the pump

The correct location of the pump is important for the operating point and maintenance point. To ensure good flow conditions, the pump should be made as close as possible to the liquid supply side. If there is enough space, the inlet of the pump should be made lower than the level of the supply liquid. Sufficient space should be left around the pump to facilitate inspection and maintenance. Allow enough space at the top of the pump to lift the heaviest parts of the pump using high level cranes and chain hoists.
Install the pump in a clean and dry place and try to avoid dirty, dusty or wet spaces.

Foundation

Pump foundations must be carefully designed to ensure that the load on the pump and its drive machine does not exceed the capacity of the soil. Almost all pumps are installed on concrete foundations, because this material is low-cost and very strong.

The installation of the pump

Successful operation and maintenance of various levels and types of pumps is one of the most critical factors: the correct installation. Correctly installed pump can be maintained in the calibration position for a long time, the pump casing and flange leakage is less, vibration is also less.

The pipeline connection

The load and stress imposed by the piping system can greatly affect the stability of the equipment. Whether the pipeline expansion or other reasons for the load will cause the shaft deflection, pump casing deformation and internal rotating parts of mutual interference. Therefore, the smaller the stress imposed on the equipment by the piping system, the better.

The pipeline cleaning

There is a gap between the rotating parts of the pump, it is necessary to prevent damage caused by abrasive particles in the new piping system. Abrasive particles deposited in the pump’s rotating gap can lead to pump downtime and very high maintenance costs. To reduce the possibility of abrasive particles entering the pump, a strainer is generally installed.

Calibration

Keep the pump at its operating temperature by introducing liquid into the pump casing. When checking calibration, the rotation of the motor and pump should be checked. The pump should rotate in the direction of the arrow on the pump casing. Drift may cause.

  • 1) Overloading of the pump bearings.
  • 2) Axial rotation of the mechanical seal back and forth, the more the seal moves, the easier it is for the overlapping seal end faces to open.
  • 3) Contact between stationary and moving parts if the offset is severe.
  • 4) Wear ring contact.
  • 5) Impeller and volute contact with each other.

Source: Network Arrangement – China Centrifugal Pump Manufacturer – Yaang Pipe Industry (www.epowermetals.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@epowermetals.com

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