the gases still had to pass in serial sequence through the muffler system the present invention adds a second passage 59 to the first passage 58 so that the gases can pass simultaneously from the discharge plenum 41 into both of the muffler chambers 46 and 48 however at the time when the discharge valve is closed the outflow from the first muffler chamber 46 is restricted by the transfer tube 55 which also has about 1 4 the cross sectional area of the passages 58 and 59 thus it is believed that after the discharge valve closes there is a reversal of flow from the chamber 46 back through the passage 58 into the discharge plenum 41 and from there to the second muffler chamber 48 through passage 59 because the discharge gases can exit from the discharge plenum 41 through both of the passages 58 and 59 and into both of the muffler chambers 46 and 48 the peak pressures within the discharge plenum are reduced thereby tending to reduce the magnitude of the noise pulses in the system the presence of the transfer tube 55 ensures the effectiveness of the filter arrangement because of its restrictive flow characteristics between the two muffler chambers 46 and 48 while the reversal of flow through the passage 58 ensures.