Tips when ordering water pumps
In the water supply and drainage industry, water pumps are an important mechanical equipment. There are many ways to order water pumps, such as bidding, market order, and complete equipment supply. At present, the order of new construction projects generally adopts the form of bidding. In order to ensure the quality of the ordered water pump, and complete the installation of the water pump according to the scheduled construction period and schedule, while taking into account the convenience of subsequent equipment operation and maintenance, the technical aspects should be paid attention to in the process of preparing bidding documents, ordering contracts and implementing procurement plans. The following questions.
1. Before ordering, the owner or user should provide the manufacturer with the plan process layout of the pump unit that has been confirmed by the design department. Mark the dimensions of the pump inlet and outlet pipe diameter, center elevation and other dimensions on the drawing, so that the manufacturer can know the plane distribution position of the pump and the direction of rotation of the impeller and motor after receiving the drawing, and at the same time, clarify the direction of the pump inlet and outlet, and the height difference between the inlet and outlet pipes. And the mutual angle (45°, 9° or 180°). For vertical shaft and mixed flow pumps, elevation views of the pump layer and motor layer should also be provided, so that the manufacturer can organize production according to the actual situation. In addition, if submersible shafts and mixed-flow pumps are ordered, the lowest water level control position in the process during pump operation should also be provided.
2. Choose the pump model to be consistent as far as possible, as a spare for each other. From the perspective of pump station operation management and maintenance, it is not easy to manage if there are too many pump models. It is generally hoped that the same type of water pump can be selected in parallel, so that no matter it is the matching of motors and electrical equipment, the installation and production of pipe fittings will bring great convenience. Priority is given to products with serialization, maturity and excellent performance. At the same time, the number of pumps ordered, specifications and models, type of conveying medium, performance parameters (flow, head, power) and operating voltage at the design operating point should be indicated in the contract. If the design parameters are not consistent with the pump sample, the user should contact the manufacturer in time, and order and organize production after signing a technical agreement.
3. According to the characteristics of the production process, combined with the pump performance curve provided by the manufacturer, select the type of pump to be ordered. For example, the head-flow relationship curve (H-Q curve) can be divided into sharp drop, flat, and hump-shaped. It is hoped that the pressure in the pipe will increase greatly when the flow rate is slightly reduced, so choose a pump with a steeper H-V curve; if the conveying medium height or pipeline pressure head will change during work, in order to avoid unstable working conditions, The H-V curve of the pump should not be hump-shaped. The power-flow relationship curve (P-Q curve) of the pump should be a smooth and peak-free curve in the working range to avoid the increase in flow and the power of the pump shaft to exceed the power of the motor itself, which will cause the motor to be overloaded and burned.
4. The material requirements of main components (such as impeller, pump shaft, shaft sleeve, pump casing, etc.) should be listed in the bidding document or contract. For example, cast iron materials are divided into spheroidal graphite cast iron, gray cast iron and alloy cast iron. For gray cast iron, it is divided into HT250 and HT300 grades. Different material grades have different chemical composition, mechanical properties and corrosion resistance, so the manufacturing cost is also different. The same kind of parts such as the impeller can be made of cast iron, cast steel or bronze. If the model and specifications of the specific material are not specified in the contract, the manufacturer may choose lower prices and lower quality materials for production. As a user, the material should be selected from the aspects of working environment, practicability and economy of the pump.
5. For the supply of water pump accessories such as elbows and reducers connected to the inlet and outlet of the water pump, the order contract should specify whether the supplier is the pump manufacturer or other installation unit, that is, it must be distinguished from other supply contracts To avoid duplication of production and supply or omissions. At the same time, it is best to request the name and quantity of special tools and spare parts for installation and maintenance of the pump when it leaves the factory. The price is included in the total purchase price. The spare parts should be interchangeable and have the same material and quality as the original pump. For common wearing parts and key parts such as shaft sleeves, pump shafts, impellers, and leakage reducing rings, manufacturers are required to provide detailed drawings of parts that can be used for machining, so as to provide basis and convenience for future operation and maintenance of the pump.
6. For the vertical axial flow pump installed in layers, the axial thrust will be generated when the pump is running, and the axial thrust is borne by the transmission device or the vertical motor. The manufacturer shall provide the specific data of the axial thrust of the pump to provide a reliable basis for the selection of the structure and specifications of the matching motor, so as to achieve the most optimized technical cooperation. In addition, the manufacturer shall also provide the weight, bearing load, force, fixing method and other data and drawings required for the layout and design of pump station equipment and structures.
7. In order to closely cooperate with civil engineering and installation, the drawings and documents provided by the manufacturer should include the installation details of the connection between the pump and the foundation and foundation bolts. Including the dimensions of the embedded parts of the water pump, the way of fixing and adjusting the position of the water pump, the dimensions of the secondary silicon pouring, and other drawings related to the civil construction, providing basis and preparation for the basic silicon pouring. Otherwise, poor cooperation will bring great difficulties to the installation of the pump and affect the construction period and schedule.
8. If you purchase the motor and the electrical control cabinet at the same time when ordering, the user should specify the pump start mode (direct start, self-accident pressure reduction start or soft start), installation method (indoor or outdoor type) and pump operation in the contract At the same time, it is necessary to monitor and alarm protection items. At the same time, it should also indicate which manufacturer's products are selected for motors, main electrical components (such as circuit breakers, fuses), programmable controllers, etc. The manufacturer should submit the control cabinet schematic diagram, wiring diagram, and PLC control ladder diagram floppy disk or CD-ROM when supplying, so that users can change the drawings in time and organize the completion materials, and do a good job of archiving relevant materials.
