The design of nonmetallic plates formed from a glass-fiber-base laminate is analyzed for potential use in intake valves of the "dry version" of rapidly reciprocating expanders, and results are cited for five types of plates. Promising use of nonmetallic plates as component parts of expander stages is noted.Provision for high efficiency and reliability of gas-distribution elements is one of the basic problems encountered in the development of reciprocating expanders. Considering the need to separate the "hot" and "cold" zones of the working chamber, preference is usually given to a direct-flow expander stage with the intake valve located in the face of the cylinder. In that case, the role of exhaust valve is played by a sliding device with exhaust ports (windows) of circular or arbitrary shape, which are located on the lateral surface of the cylinder in the zone of bottom dead center (BDC). With this gas-distribution system, maximum possible channel sections are achieved in the seat of the exhaust valve; with a fixed section in the slot, this makes it possible to reduce the displacement of the valve plates h va , their impact velocities with the seat w s and limiter w l , and the stresses σ in the valve plates to the maximum extent possible.For this design of the expander stage, it is expedient to replace the metallic valve plates with nonmetallic ones (formed from a pure, or copper-coated glass-fiber-base laminate), which offer a number of advantages:• low noise level during operation of the intake valves;• high heat resistance of the plates; this makes it possible to use them in expander-generator units with a gas temperature falling within the range from 150 to 300°C at the inlet; • airtightness of the closed valves, and absence of seat and limiter wear, as well as light weight of the nonmetallic plates predetermine the expediency of their use in lubricant-free stages in units with increased rotational speed of the shaft and moderate piston speed; • a very high level of operational safety, since breakdown of the valve plates will not result in even greater damages when components of the driving mechanism, the cylinder-piston groups (CPG), and expensive greaseless piston and rod seals malfunction; and • the simplicity with which the nonmetallic valve plates are fabricated, and also their maintainability not only enhance the reliability and longevity of the working components of the CPG, but also make it possible to lower operating expenditures considerably.

At present the Sibkriotekhnika Joint-Stock Company (AO), Kompressor Scientific ,, Production Association, Kompressory BS NPTs, and a number of other organization produce compressors with low capacity in vertical, Y-shaped, and W-shaped versions intended for use in air conditioning, medicine, in transport and other branches of the economy [i]. A distint, uishing feature of these machines is their reliable and economical operation without lubrication, not only of the piston t, "oups but also of elements of the motive mechanism. They are therefore promising elements in designing multipurpose expanding machines whose application is most useful as decompressors, pneumatic motors, or independent, ecologically safe decompressor and compressor plants.The production of such machines envisages the use of a single unified compressor base which enables the producing enterprise with minimal production costs and within a short time to broaden the assormaent of products.The substance of the technical solution will be illustrated on the example of a separate series of multi-row piston engines whose design diagram is shown in Fig. 1.Piston 1 provided with seals or packing rings carries out a reciprocating motion without lubrication in cylinder 2 which on its periphery has the composite chamber 3 (pressure and temperature of the emerging gas is Pt', Tf, respectively). On the end face of the cylinder there are one or several single-type normally open self-acting inlet valves 4 whose shutting element moves within the range 0 < h < hva. The working gas (air) with the initial parameters Pi, Ti is fed to the inlet chamber 5 from the pneumatic mains of the enterprise or from a compressor stage of the plant itself.The cycle of the multipurpose expanding machine (MPEM) is presented in Fig. 2. The theoretical decompressor cycle 1-2-3-4-5-1 intended for obtaining the required final temperature of the gas Tf upon its expansion within the pressure range Pi-Pf is basic, for ensuring the mass flow rate of the gas m and the refrigerating power Q = Cpffa(T/-Tf), where cp is the heat capacity of the gas. In this case, when the piston moves from upper dead center (UDC) to the side of the shaft, the cylinder is filled with fresh gas via the open inlet valve (processes 1-2), and this is accompanied by an increase of the pressure gradient Ap, = Pi --Pc('P) that is due to the change of the instantaneous speed of the piston. At point 2 the gas force Fg, proportional to Ap2, exceeds the force of the valve spring Fsp, and in consequence the valve is automatically closed and the working chamber becomes closed, i.e., it is isolated from the inlet and outlet chambers. Further movement of the piston on the section 2-3 (the process of expansion) increases the volume of the working chamber, the pressure in it decreases from P2 to P3 with the corresponding lowering of the temperature. At point 3 the moving piston uncovers the exhaust windows 6 (see Fig. I) in the lateral surface of the cylinder in the zone of the lower dead center (LDC), and that leads to an abr...

A promising line for upgrading compressors and expansion machines is the use of unlubricated cylinder-piston units, and sometimes other parts of the moving mechanism. This raises a problem over efficient and long-lived seals, which are made of nonmetallic materials having low elastic moduli E.Calculations and test results show that the maximum pressure differences across a single sealing ring are Ap < 3 MPa in the various stages, which means that the low elastic modulus implies that the rings may be deformed.When the rings deform, there are changes in the parameters of the slots between the surfaces through which compressed gas flows: piston ring-cylinder or piston-ring-end surface of piston groove.In general, gas leaks through the seal on three channels (Fig. 1, in which Pl and P2 are the pressures at the inlet and outlet from the slot):-through the ring section fr = ff'Dc~n between the cylinder 3 and the sealing ring 2 with a nominal gap in the slot ~n = ~r; -through the end diffuser channel fe = ~Z(Dc -bg)Sn between the ring and the groove in the piston I with nominal gap in the slot 5 n = ~e; and -through the rectangular section in the sealing ring joint fj [1]. Calculations on the flow rate through the shot usually involve replacing these channels by a single section subject to the condmon f = fr + fe +fj =/r'Dc~n" The nominal equivalent gap 5 n is determined by experiment. To simplify the calculations, one usually assumes a linear variation in the pressure along this channel, which has a constant area of cross section f. The condition f = constant essentially establishes that the gap 5 n is independent of the pressure pattern in the gas flow region. That assumption is correct for metal rings 9 From [2], the effects of the ring height h and gap 5 n on the vertical distribution over the ring are negligible, but when one uses nonmetallic rings, one has to assume that ~n = f(A'), and consequently that the area of the annular slot f* varies over the height of the ring, which may have a substantial effect on the pressure distribution over the height of the ring [2], and also on the actual gas flow rate through the slot and the type of wear on the sealing rings. In the installed state (Fig. 2a), the cross section of the sealing ring is a rectangle of dimensions b x h; with a uniform pressure p on all the faces of the ring, which has previously been pressed on to the cylinder by the expander, the equivalent radial gap ~n may be taken as constant over the height h of the ring. When a compressor or expansion machine operates, there is a gas leak through f*, and the load distribution on the ring corresponds to that shown in Fig. 2b, which we assume for determining the deformation of nonmetallic sealing rings.In the elastic strain range [1, 3], the forces act independently, and the strain in the piston ring from the various factors is equal to the sum of the strains from each of them separately. We estimate the dependence of the sealing ring strain on the gas pressure difference Ap. The ring is firmly pressed on to the...