Find the selection criteria for pumps

First, here is some of the design requirements for a centrifugal pump: 1 General requirements 1.1 The pump and its auxiliary equipment should be suitable for installation and operation in outdoor environments. 1.2 The pump shall have a stable characteristic curve, on which the allowable operating range of the pump is indicated; the normal operating point of the pump shall not exceed the point of optimal efficiency and shall be as far away as possible from the minimum flow rate point. 1.3 The seller shall ensure that the performance of the pump, including efficiency, flow rate, head, power consumption, and the required net positive suction head, meets the specified requirements. 1.4 The available NPSH(a) should be at least 0.5 m greater than the required NPSH(r), without considering any correction factors for hydrocarbon liquids. 1.5 All components shall have a proven track record of successful use under similar operating conditions; prototypes or trial products shall not be used without the buyer’s consent. 2 Pressure-bearing parts 2.1 The design pressure of the pump casing shall be equal to the sum of the highest inlet pressure and the maximum pressure difference that the pump can achieve; if the highest inlet pressure is lower than atmospheric pressure, it shall be taken as atmospheric pressure. 2.2 For pumps operating at temperatures above 0°C, their design temperature should be determined by taking the highest temperature that may be encountered and adding 10°C to it. For pumps operating at temperatures equal to or below 0°C, their design temperature should be based on the lowest operating temperature that may be encountered. 2.3 At operating temperatures, when transporting media with a specific gravity of less than 0.7, which are flammable, explosive, or toxic, pumps with a radial split design should be used. 2.4 The pump should be designed with a back-door structure, allowing the impeller, shaft, shaft seal, and bearing components to be removed without having to move the inlet and outlet flange connections.

Cooling issues: The transportation of high-temperature media places higher demands on the pump’s structure, materials, and auxiliary systems. Below, we discuss the cooling requirements associated with different temperature levels, as well as the types of pumps suitable for use in such applications: 1. For media with temperatures below 120°C, a dedicated cooling system is usually not required; instead, the medium itself is used for lubrication and cooling. Such as DFL(W)H chemical pumps, DFL(W)PH shielded chemical pumps (for temperatures above 90°C, the protection class of the shielded motor should be H grade) ； The standard version of DFCZ and IH chemical pumps can achieve an upper temperature limit of 140°C to 160°C thanks to their suspension structure℃ ； The maximum operating temperature for IHF fluoroplastic pumps can reach 200℃ ； Only the ordinary CQB magnetic pump is designed for use at temperatures not exceeding 100°C. It is worth noting that media that are prone to crystallization or contain particles should be equipped with a sealing surface flushing pipeline (interfaces are provided during design). 2. For media with temperatures above 120°C and below 300°C, a cooling chamber is generally required on the pump cover, and the sealing chamber should also be connected to coolant (a double-end face mechanical seal is necessary). When it is not allowed for coolant to penetrate into the medium, the medium itself should be cooled before being fed in (this can be achieved using a simple heat exchanger). Currently, the company offers DFCZ-type chemical process pumps, GRG high-temperature pipeline pumps, and HPK hot water circulation pumps (under development) for selection; in addition, the CQB-G high-temperature magnetic pump can be used for high-temperature media up to 280°C. 3. For high-temperature media above 300°C, not only the pump head section but also the suspension bearing chamber requires a cooling system. The pump structure is generally of a central support type, and metal bellows-type mechanical seals are preferred, although they are expensive (their cost is more than 10 times that of ordinary mechanical seals). Currently, DFAY centrifugal oil pumps can operate at temperatures up to 420°C (under development). Sealing issues: Zero leakage is the perpetual goal for chemical processing equipment, and it is precisely this requirement that has led to the increasing use of magnetic pumps and shielded pumps. However, there is still a long way to go before true leaklessness can be achieved, such as the lifespan issues of magnetic pump isolation sleeves and shielded pump shielding sleeves, the pitting problem of materials, and the reliability of static seals, among others. Here is a brief introduction to some basic aspects of sealing: 1. Sealing types 　For static sealing, there are usually only two types: gaskets and seals, with O-rings being the most widely used type of seal ； For dynamic sealing, chemical pumps rarely use packing seals; mechanical seals are preferred. Mechanical seals come in single-face and double-face types, as well as balanced and unbalanced versions. Balanced mechanical seals are suitable for sealing high-pressure media (typically those with a pressure greater than 1.0 MPa). Double-face mechanical seals are used mainly for media that are high-temperature, prone to crystallization, viscous, contain particles, or are toxic and volatile. An isolation fluid must be injected into the sealing chamber using double-face mechanical seals, and its pressure is generally 0.07–0.1 MPa higher than the pressure of the medium. 2. Sealing materials: Fluororubber is generally used as the static sealing material for chemical pumps, while polytetrafluoroethylene is employed only in special cases ； The material selection for the stationary and rotating rings of mechanical seals is quite important. It’s not true that one combination of cemented carbide materials is always the best; high costs are one issue, but it’s also unreasonable if there is no difference in hardness between the two materials. Therefore, it’s best to choose materials based on the characteristics of the medium being handled.

Latest standards for pumps: JB/T 6880.2-2008 – Cast steel components for pumps; GB/T 3214-2007 – Methods for determining the flow rate of water pumps; GB/T 3215-2007 – Centrifugal pumps for the petroleum, heavy chemical, and natural gas industries; JB/T 4297-2008 – Technical requirements for painting pump products; JB/T 6435.1-2006 – Small multi-stage centrifugal pumps: Types and basic parameters; JB/T 6879-2008 – Tolerances for dimensions of the flow-through parts of centrifugal pump castings; JB/T 8059-2008 – Technical requirements for high-pressure boiler feed pumps