Volumetric machines Introduction to fluid flow machines. Machines that change the volume of a certain amount of liquid in the machine are called positive displacement machines. It is also called a punching machine. The machine that generates mechanical energy is called a piston engine.
A positive displacement pump has an expandable cavity on the suction side and a decreasing cavity on the pressure side. The liquid flows through the pumps when the cavity on the suction side expands and the liquid flows out of the outlet when the cavity collapses. Volume is a constant for each operating cycle.
Positive displacement pumps are mainly used for low pressure applications and are designed for a maximum pressure of 18 to 20 bar. With a volumetric pump, the power flow rate is constant as the pressure varies, while the flow rate with a volumetric pump does not change with the pressure variation.
A volumetric pump causes a liquid to move by trapping a fixed amount and forcing (displacing) the trapped volume in the drain pipe. Some positive displacement pumps use an expandable cavity on the suction side and a decreasing cavity on the pressure side.
Positive displacement pumps are widely used to pump high viscosity fluids such as oil, paint, resin or food. They are preferred in all applications where precise dosing or high pressure is required.
Piston pumps are known as positive displacement pumps because they deliver a fixed amount of liquid at each stroke. The pressure drop keeps the drain valve closed as it cannot open downward.
There are four common types of PD pumps: internal equipment, external equipment, timing lobes, and vanes. Most PD pumps can be customized for a wide variety of applications, but some types are better suited than others for certain conditions. The first evaluation in all applications is the condition of the pump.
Explanation: The offset can be negative because it defines a change in the position of an object as it accurately follows its direction. Then return to the original position in the opposite direction.
The best examples of positive displacement pumps are pistons, pistons, diaphragms, gears, pistons, propellers and blades. Piston and piston pumps are used for pumping low viscosity fluids, spray painting, oil pumping and heavy scrubbing operations. A common pump is used in low viscosity fluids, when filling and transferring fuel, etc.
Volumetric pumps: A pump is a machine used to move liquids from a low point to a high point. The operation of the volumetric pump is achieved by increasing or decreasing the volume in a space through which the liquid (or gas) physically moves. The liquid is discharged to the piston and the intake valve remains closed.
Displacement flow meters (PD) measure the flow rate of a liquid or gas by dividing the fluid into measured solid volumes (final stages or liquid volumes). With adequate pressure and temperature compensation, the mass flow can be accurately determined.
Centrifugal pumps exploit the centrifugal effect of the rotating impellers to move the liquid. The main difference between centrifugal pumps and positive displacement pumps is that, unlike centrifugal pumps, positive displacement pumps move the liquid at the same speed regardless of the pressure at the inlet end.
Different types of positive displacement pumps
Compensation. It is always positive and equal to the absolute value or the magnitude of the displacement. If we follow the rule of always subtracting the first position from the second, the sign is always positive when the shift is to the right and negative when the shift is left.
Explanation: The centrifugal pump is not a positive displacement pump. Piston pumps move fluid backward from a piston, piston or diaphragm into a fixed volume or cylinder by constant motion.
A positive displacement pump should never run against closed valves on the outlet side of the pump, it does not have a stop head like centrifugal pumps. A safety or safety valve on the delivery side of the volumetric pump is essential. The safety valve can be placed inside or outside the pump.
A variable displacement pump is a device that converts mechanical energy into hydraulic (liquid) energy. The displacement or amount of liquid delivered per revolution of the pump input shaft can be changed while the pump is running.
Pressure, temperature, flow rate and fluid properties determine the correct type of PD pump.