From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Tests conducted on two HERTZMARK air compressors.
| Identifier | WestWitteringFiles\W\September1931-November1931\ Scan023 | |
| Date | 3rd October 1931 | |
| ORIGINAL To R.{Sir Henry Royce} From Ha/Aln. c. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} c. to Rg.{Mr Rowledge} E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} HERTZMARK AIR COMPRESSORS. X4644 We have now made tests on two of these units, a large one weighing 8 lbs. 3 ozs. and a small one weighing 4 lbs. 0 ozs. A drawing of the smaller compressor is attached, the large one is mainly similar but has a square flanged base and a screw-in cover in the bottom. The compressors are made mainly of cast aluminium and are of the "single-acting" type i.e. compression on every up stroke, the direction of rotation being immaterial. Air enters the crankcase via a gauge fitted in the filler cap through which a working quantity of oil (we used F.2) is poured before starting. The piston is attached to a crosshead working in guides and having a horizontal slot in which slides a bronze block carrying the crankpin. Incidentally, this gives pure harmonic motion to the piston. A non-return ball valve and spring loaded relief valve together with a screw-down needle valve release are carried in the head. This last item is on the delivery side of the non-return valve so that if not properly closed it will discharge the air bottles to which the compressor delivers, starting with the oil which is put into them for sealing purposes. The release has a hexagon head and on each compressor a spanner was needed to close them properly, which is perhaps a good safeguard against their coming loose. The general finish of the compressors is moderately good, but they do not appear to be easy to dismantle and reassemble without undergoing minor damage. It is intended that these compressors should be driven from the engine camshaft and deliver to air bottles which act as a storage for starting and other uses. In each case therefore, the compressor was arranged delivering the air bottles of known capacity (two being used in parallel) with entrances at the bottom. A certain amount of oil was put in to act as a seal on the non-return valves of the compressor. Allowing for this, the remaining air space available for storage was .413 cu. ft. (total). The compressors were run at 1125 R.P.M. which represents normal camshaft speed of Kestrel engines. Attached are curves showing the pressure rises against time. From these it will be noted that the rate of pressure rise does not fall off greatly throughout the pressure range which shows that the inherent compression ratio of the compressors is very much higher than the 14.43:1 represented by raising the air from atmospheric pressure to 200 lbs/sq.in., the limit to pressure rise being obtained by means of a relief. This limit was reached at just under 200 lbs. in the case of the larger compressor, which is not marked, but the smaller one though marked "200 lbs" went above this pressure off the scale of our gauge, so that we are not sure whether the relief valve operated or not. | ||