Positive displacement pump

It should be, why can the pressure reach infinity?

Not all liquids are incompressible (rigid); volume pumps operate under backpressure, and theoretically this pressure can be very high, but strength, power, and leakage issues significantly limit this trend as the pressure increases!

This post was last edited by Zhongheng Pump Industry on 2021-1-16 at 16:59. Hello, original poster! Positive displacement pumps are also known as “volumetric pumps”. Pumps that apply energy to a fluid periodically through several enclosed liquid-filled chambers (such as cylinders), thereby increasing the liquid pressure directly to the desired value, including reciprocating pumps, rotor pumps, etc. 　　 1. Reciprocating pump A reciprocating pump is a general term for piston pumps, plunger pumps, and diaphragm pumps; it is one of the most widely used types of positive displacement pumps. Based on the driving mechanism, reciprocating pumps can be divided into three categories: motor-driven pumps (powered by electric motors), direct-acting pumps (powered by steam, gas, or liquid), and manual pumps. A reciprocating pump is a fluid transfer machine that supplies energy to a liquid in the form of pressure energy through the reciprocating motion of a piston. 　　(1) Piston pump The main components of a piston pump are the pump cylinder, piston rod, and single-phase intake and discharge valves. The space between the piston and the valve inside the pump cylinder is the working chamber. 　　As the piston moves from left to right, the volume of the working chamber increases, creating a low pressure; the suction valve is pushed open by the liquid outside the pump and enters the pump cylinder, while the discharge valve closes due to the pressure of the liquid in the discharge pipe. The piston reaching the right endpoint completes the intake stroke. As the piston moves from right to left, the liquid inside the pump cylinder is compressed, increasing its pressure; this pressure pushes the discharge valve open and forces the liquid into the discharge pipeline, while the suction valve closes. The piston moves to the left endpoint, completing the discharge process and thus finishing one working cycle. The piston moves back and forth in this manner, causing the liquid to be intermittently drawn into the pump cylinder and discharged into the delivery pipeline, thereby achieving the purpose of fluid transfer. 　　(2) Metering pump A metering pump, also known as a proportional pump, features the ability to regulate flow rate by changing the stroke length of the plunger. When it is necessary to deliver a liquid at a constant flow rate, it is possible to achieve this conveniently and accurately by adjusting the eccentricity of the eccentric wheel, thereby changing the plunger’s stroke length. Sometimes, several liquids can also be delivered or mixed in proportion by using one motor to drive multiple metering pumps. 　　(3) Diaphragm pump A diaphragm pump can be used when transporting corrosive liquids or suspensions. A diaphragm pump is essentially a piston pump; its structural feature is that an elastic membrane is used to separate the liquid to be transported from the piston, thereby keeping the piston apart and protecting both the piston and the pump cylinder. The parts of the diaphragm on the left side that come into contact with liquid are made of corrosion-resistant materials or coated with a corrosion-resistant substance ； The right side of the diaphragm is filled with water or oil. As the plunger moves back and forth, it forces the diaphragm to bend alternately to both sides, drawing in and discharging the liquid to be transported. The elastic diaphragm is made of corrosion-resistant rubber or metal sheets. 　　Diaphragm metering pumps can be used to deliver toxic, flammable, explosive, and corrosive liquids in precise quantities. 　　 2. Rotary Pump A rotary pump, also known as a rotating pump, belongs to the category of positive displacement pumps. Their working principle relies on the rotation of one or more rotors inside to draw in and discharge fluid. Gear pumps and screw pumps are commonly used in the petrochemical industry. 　　(1) Gear pump 　The externally meshing gear pump, which is commonly used in the petrochemical industry, has a pump casing divided into a suction chamber and a discharge chamber that are not connected to each other. As the gear rotates, the teeth of the two wheels in the suction chamber push apart from each other, creating a low pressure that draws in the liquid ； Then the liquid is confined in two paths between the tooth pockets and the housing, and as the gears rotate toward the discharge chamber, the teeth of the two gears there interlock to generate high pressure, which drives the liquid out. The flow rate and head of this type of pump fluctuate somewhat, and it is noisy and vibrates. In recent years, internal gear pumps have been gradually adopted due to their stable operation, although they are more complex to manufacture. 　　Gear pumps have a low flow rate but high head, making them suitable for transporting viscous liquids and even paste-like materials; however, they cannot handle suspensions containing solid particles. 　　(2) Screw pumps　Screw pumps consist of a pump casing and one or more screws. The working principle of a twin-screw pump is very similar to that of a gear pump; it relies on intermeshing screws to pump liquids. When a higher head pressure is required, a longer screw can be used. 　　Screw pumps feature high head, high efficiency, smooth operation, and low noise, making them suitable for transporting high-viscosity liquids. 　　The operating characteristics of a rotor pump are similar to those of a reciprocating pump. At a certain speed, the pump’s flow rate remains constant regardless of the pump’s head; it has self-priming capability, so no priming is required before starting, and bypass is used to regulate the flow rate. Due to the limitations in the tightness of rotating components, the head pressure of rotary pumps is lower than that of reciprocating pumps. I hope this helps you. If you have any questions regarding pumps, feel free to contact me at any time. My phone number is: 13313170275 (same as my WeChat ID)