Striker travel in a pneumatic machine during filling and discharge of the working chamber

Abstract

Other authors [1][2][3] have determined the path length of the travel of the striker during filling and discharge of the working chambers of pne-m-tlc mechanisms by solving a system of equations characterizing the motion of the striker and the thermodynamic processes occurring in the working chambers.It is difficult to determine the path length of the striker in these intervals, because this system of equations cannot be solved in finite form. Solution is effected by means of successive approximations with numerical integration.For this reason available design experlence is often used as a basis and values are assigned to the displacements of the striker during admission and exhaust and are then corrected during development of the machine. However, the development process is costly and time-cons,~4ng.We will give equations in this article for the lengths of the admission and exhaust strokes of theworklng chamber, obtained by simultaneous solution of equations relating the air pressure in the chambers to the admission and exhaust times, together with equations of motion of the striker based on the theorem of B. V. Sudnlshnlkov concerning the motion of a mass under'the influence of a force which is given as a function of time [4].Let us consider this problem in connection with the operating cycle realized in pneumatic punches and machines for driving piles and grounding electrodes.These are valveless machines in whlch the rear chamber is always in communication with the pneumatic mains while the forward (controlled) chamber is connected periodically via the rear chamber when the inlet port is open.We are to determine the displacement of the striker from the moment of opening of the intake port to the extreme forward position, or from the moment of opening of the outlet port to the extreme rearward position.We make the following assumptions:the parameters of the air in the supply mains are constant; there is no friction between the moving parts; the movement of the frame during the cycle is small in comparison with the travel of the striker; during the parts of the cycle in which the controlled chamber is filled and exhausted, the time dependence of the air pressure in the working chambers is linear; and the cross sections of the inlet and exhaust channels reach their critical values instantaneously.With these assumptions, in Fig. 1 we show part of the operating cycle of a machine during filllng (a) and exhaust (b) of the controlled chamber.Curves 1 and 2 represent the pressures in the rear and forward chambers; u is the moment of admission, b that at which the forward chamber is cut off from the mains, c that of transition from supercritlcal to subcrltical flow, d that of impact, and e that of onset of exhaustion.Indicatordlagrams of similar machines show that the moment of impact arrives at the beginning of the subcrltlcal flow and the real value of the pressure in the controlled chamber at this moment is nearly equal to the critical pressure.Therefore we assume that the pressure in the controlled chamber becomes ...

The operational cycle of a percussive pneumatic machine

“…Here Tf and T d are the dimensionless times of filling and discharge of the front chamber, found as in [4,6].…”