Rocking piston compressors, diaphragm compressors and vacuum pumps all use the reciprocating motion of a connecting rod to produce increased pressures within a control volume, such as a cylinder. The amount of stroke of the connecting rod determines the compression ratio for the fixed control volume. Therefore, variations in the length of the connecting rod assembly translate to variations in the compression ratio and ultimately variations in compression or vacuum pump performance. These performance variations may include changes in flow, amperage draw, maximum pressure output or vacuum levels.
A typical design for a connecting rod assembly includes a connecting rod, a diaphragm or cup and a retainer to hold the diaphragm or cup on the connecting rod. An example of a typical currently-available connecting rod assembly for a diaphragm compressor is illustrated in FIGS. 1-3A. A connecting rod assembly for a rocking compressor or a vacuum pump is shown in FIG. 3B. Specifically, a connecting rod assembly is shown at 10a which includes a connecting rod 11a, a diaphragm 12a and a retainer plate 13a. The retainer plate 13a sandwiches the diaphragm 12a between the retainer plate 13a and a disk portion 14a of the connecting rod 11a. Because the connecting rod assembly 10a must be serviceable with common hand tools, threaded fasteners, such as screws 15a are used to secure the retainer plate 13a to the disk portion 14a of the connecting rod 11a. The connecting rod 11a includes a crank end 16a that is connected to the disk portion 14a by way of a middle section 17a.
The problem associated with the diaphragm rod assembly 10a is best illustrated in FIGS. 3A and 3B. Specifically, the overall length of the assembly 10a is dependent upon three separate parts: the overall length or height of the connecting rod 11a, the thickness of the diaphragm 12a (see FIG. 3A) or cup seal 12b (see FIG. 3B) as well as the thickness of the retainer 13a or 13b. As a result, a rod assembly having an intended length or height of 51/8" may have a height variability range exceed 0.02". The specific variability range for the assemblies 10a and 10b illustrated in FIGS. 1-3B is 0.023". This variability range is significant in that it is found that in excess of 50% of the possible variability of the compression ratio is caused by the height variability of the rod assembly.
Yet another factor that compounds this problem is that the diaphragm 12a or cup seal 12 must be serviceable using common hand tools readily available to the unskilled equipment operator. Further, serviceability is important in that the retainer plate and diaphragm must be easily removed for replacement of the diaphragm. One problem associated with currently-available connection rod assemblies is that the overall height or length of the assembly changes when the diaphragm is changed. Specifically, referring back to FIGS. 1-3B and, specifically to FIGS. 3A and 3B, it will be noted that the thickness of the diaphragm 12a or cup seal 12b can affect the overall height of the assembly if the diaphragm 12a or cup seal 12b prevents the retainer 13a, 13b from engaging the disk portion 14a, 14b of the connecting rod 11a, 11b.
Therefore, there is a need for an improved connecting rod assembly wherein the assembled height variability is reduced as much as possible. Further, there is a need for an improved connecting rod assembly which is quickly and easily serviced and wherein the changing of the diaphragm or cup seal does not affect the overall height of the assembly. Still further, there is a need for an improved connecting rod assembly that can serve as al replacement for existing connecting rod assemblies and existing rocking piston compressors, diaphragm compressors and vacuum pumps.