Effect of Valve Design On Reciprocating Compressor Performance

In air piston compressors, the effects of the valve system, which is responsible for taking the air into the cylinder and compressing it, increasing the pressure and pushing it out of the cylinder, on the compressor performance were examined experimentally in this study. It has been determined that the power drawn by piston compressors varies depending on the spring tensions of the suction and discharge valves, and as a result of the experiments, it has been observed that when the spring tensions are reduced, the power drawn by the compressor decreases.

The design parameters of the suction and discharge valves used in piston air compressors directly affect the operation of the compressor. In valve system, the suction side is responsible for taking the air into the cylinder, and the discharge side is responsible for transferring the air out of the cylinder after it is compressed and pressurized in the cylinder.

Piston compressors are generally used to provide the necessary compressed air to pneumatic tools and air-powered equipment. The main elements of a piston compressor are the crankcase, the crankshaft in the crankcase, the connecting rods, the pistons connected to the connecting rods, the piston pins and bearings, the cylinders in which pistons move, the valve systems that allow the air into the cylinders and pressed out, and the cylinder on the valve systems. The locations of these elements are shown in Figure 1.

This study was conducted on concentric valves and the valve parts are shown in Figure 2. In concentric valves, air is taken into the cylinder by vacuum effect created by the movement of the piston from Top Dead Center to Bottom Dead Center. The discharge side of the valve is in the closed position during air suction. The absorption of air is completed when the piston reaches Bottom Dead Center, and the air in the cylinder is compressed during its movement from Bottom Dead Center to Top Dead Center. At a certain point in the compression stroke, air is transferred out of the cylinder by opening the discharge side of the closed suction and discharge valves. While the discharge side of the valve is open, the suction side is closed.

Within the scope of the study, a three-stage 40bar reciprocating compressor used (Figure 3). The compressor, whose air inlet and outlet to the cylinders are provided by a concentric valve system, is driven by a 4P electric motor with a power of 30 kW. In the first stage of the compressor, two compression springs and three suction springs shown in Figure 1 are connected in series. One each of the suction and discharge valves, which open and close according to the direction of air passage, are mounted. By changing the number of springs in the valve, the cylinder internal pressure change and the compressor power change were observed. In order to calculate the power drawn by the compressor, ± 0.05% F.S. was used in the test setup. Torque meter with measurement accuracy of ± 0.1% F.S. a pressure transmitter with measurement sensitivity was used. For in-cylinder pressure measurements, pressure sensors were mounted by opening 5 metric threads near the discharge area of the valve. The pressure transmitters and torquemeter used are shown in Figure 4. The data were recorded on the computer using the Dewe45 data logger and Dewesoft software.