Buffer tank and safety valve

Buffer tank is reciprocating pump and metering pump ancillary equipment, used to reduce the uneven flow in the pipeline, divided into the suction buffer tank and the discharge buffer tank. Inhalation buffer tank role is to reduce the suction pipe flow non-uniformity, reduce inertia losses and improve pump suction performance. The role of discharge buffer tank is to reduce discharge pipe flow unevenness, to avoid over-flow generated to meet the needs of the process. The structure of the buffer tank has two types of direct contact and diaphragm. (1) Direct contact buffer tank Direct contact buffer tank, also known as atmospheric buffer tank, filled with atmospheric gas, gas and liquid direct contact, as shown in Figure 2-72. Filled with gas generally air, when the transport of flammable liquids should be filled with inert gas. In addition, because the gas is in direct contact with the delivery liquid, part of the gas is dissolved in the liquid (which is dissolved at high pressure) and is taken away by the liquid. So there is an injection valve in the buffer tank or gas injection equipment to supplement the air. (3) the selection of buffer tank ① discharge buffer tank selection When the flow of reciprocating pump flow can not meet the needs of the process can be installed and discharged Buffer tank. Within the allowable range (usually ∞-0.005 ~ 0.04), the specific value according to the requirements of use. Discharge buffer tank volume sulfone according to formula (2-32) calculation. Where D-plunger or piston diameter m; L-plunger or piston stroke length, rn; Pd-pump outlet pressure in MPa; Pra-pump out l: 1 total resistance loss in the line (excl. Acceleration head ), MPa; Pgas - buffer tank inflation pressure, generally 60% of the pump outlet pressure, MPa; Q - process requirements allow flow non-uniform; wide pulsation coefficient, a single cylinder pump 1.1, 0.42, three-cylinder pump a coffee 0.05. ② suction buffer tank installed suction suction buffer tank, pump suction pressure can be uneven if the coefficient such as control at 1% to 5%. The general decision by the pump plant whether to install suction buffer tank, as well as the buffer tank structure and specifications and other parameters. Safety valve safety valve is also an important ancillary components of positive displacement pump, each positive displacement pump must be provided with safety valve, if the pump can be provided separately. A positive displacement pump safety valve, normally installed in the pump outlet header, fitted with a discharge buffer tank shall be installed in front of the first valve f-1 (ie shut-off valve) behind the discharge buffer tank. (1) Performance parameters of safety valve ① Sealing pressure Pm The sealing pressure Pm of the safety valve shall be equal to the allowable maximum discharge pressure Pd of the pump (refer to the pressure of liquid after the reciprocating pump refers to the multi-cylinder pump or the discharge buffer tank). If the actual operating pressure of the pump is lower than the allowable maximum discharge pressure, the safety valve shall adjust the seal pressure according to the actual operating pressure. Under the sealing pressure, the safety valve shall not have any leakage. ② safety valve jump set pressure to set the pressure relief valve also known as safety valve opening pressure. When the pump discharge pressure is greater than the starting pressure pk, the safety valve that is open, the pressure released to a predetermined level. Reciprocating Pump Safety Valve Start-Up Setting Press values ​​are shown in Table 2-15. Rotor pump safety valve start-up set pressure pk can be found in Table 2-16. ③ safety valve back pressure ph When the pump discharge pressure is less than the relief valve back pressure, the safety valve is closed. The safety valve on a move obviously no back pressure ph. Table 2.15 Reciprocating Pump Safety Valve pk, ph Recommended Value MPa (G) Safety Valve Installation Position Safety Valve Seal Pressure P. Safety valve opening pressure sound k Safety valve recoil pressure m Multi-cylinder pump After draining the buffer tube or after the tank ≤1.0 Pm + (0.2 ~ 0.3) Pk- (0.4 ~ O.5)> 1.0 (1.O8 ~ 1.15) pm (0.87 ~ O.82) pk single cylinder pump discharge buffer tank or rather ≤1.0 Pm + (0.3 ~ 0.5) Pk- (0.5-0.6)> 1.0 (1.1-1.3) pm 72) Pk Table 2-16 Pk, Ph Recommended Values ​​for Safety Valve for Rotor Pump MPa (G) Safety valve mounting position Pressure relief valve seal pressure Pm Relief valve opening pressure pk Relief valve return pressure pn Pump outlet and shut-off valve ≤ 1.0 Pm + 0.2 Pk-0.4> 1.0 1.1pm 0.85pk (2) Membrane buffer tank Membrane buffer tank also known as pre-pressure buffer tank, the accumulator type, the use of diaphragm to separate the gas and liquid (see Figure 2 -73), work must be pre-filled with a certain pressure of gas (air or nitrogen). Diaphragm buffer tank and direct contact buffer tank compared to its small size, and gas and liquid do not touch, can guarantee the nature of liquid transport. Unless otherwise specified, a diaphragm buffer tank is recommended. Diaphragm buffer tank sub-diaphragm type and double diaphragm type two. Single diaphragm buffer tank diaphragm material stainless steel, PVDF, rubber, etc .; double diaphragm buffer tank is commonly used in metal diaphragm should not be used occasions, diaphragm material PVC, glass fiber reinforced polytetrafluoroethylene and so on. (2) Types of Safety Valves Safety valves for positive displacement pumps have two types of spring-loaded safety valve and one-time safety valve. Their performance is shown in Table 2-17.

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