Compressors double-acting cylinders

After all the previous statements, it would seem very difficult to select a piston. speed. For someone without direct experience, the following guidelines can be used as a starting point. Actual gas compressing experience should be solicited when a new compressor for the same gas is being eonsidered. These values will apply to the industrial process type of compressor with a double-acting cylinder construction. For horizontal compressors with lubricated cylinders, use 700 feet per minute (fpm) and for nonlubricated cylinders use 600 fpin. For vertical compressors with lubricated cylinders, use 800 fpm and for nonlubricated cylinders use 700 fpm. 

An additional capacity control method is the unloader. This method can be used in conjunction with clearance pockets to extend the range of control to zero capacity. On double-acting cylinders, unloading the individual sides one at a time will provide a two-step unloading of the cylinder. On multicylinder arrangements, the cylinders can be unloaded one at a time providing as many steps as cylinders operating in parallel. The unloaders can also be used to totally unload the compressor, as is necessary for electric motor driver startup. 

Another variation is the tandem cylinder. The tandem cylindet arrangement again allows two stages of compression on the same compressor throw but uses two double-acting cylinders separated by a second distance piece. This arrangement is usually used in low rod load applications where higher capacity is required. 

Late in the field life it is desirable to compress the 100 MMscfd for the example field downstream of the separator from 800 psig at 100°F to l.(XX) psig. An engine-driven separable compressor is available from surplus. The engine is rated for 1,600 hp at 900 rpm. Horsepower is proportional to speed. The compressor frame has six 7-in, bore by 6.0-in. stroke double-acting cylinders with a minimum clearance of 17.92%, a rod load limit of 25,000 lb, and rod diameter of 1.75 in. Assume k = 1.26, Z, -0.88, and Zd = 0.85. 

Using this technique, I once discovered that one end of a compressor s two double-acting cylinders had a defective unloader. This failure reduced the capacity of the affected cylinder end by 40% and hence reduced the compressor s capacity by 10% (i.e., 40% x 25%). 

For a reciprocating compressor, at end of a discharge stoke, the piston does not travel all the way to the end of the cylinder. The volume between the piston and the cylinder end at end of the discharge stoke is called the clearance volume. For a double-acting cylinder, there are two clearance volumes, one at the cylinder crank end and the other at the cylinder head end. 

FIG. 10-86 Two -stage double-acting compressor cylinders with intercooler. 

Figure T1 -8. Valve-in-piston double-acting compressor cylinder. Couriesy of Dresser-Rand Company.)...

Example 13-1. Surge Drums and Piping for Double-Acting, Parallel Cylinder, Compressor Installation... 

Compressor data Single-cylinder, double-acting, 10-in. bore, 14-in. stroke, piston displacement of 382 cfm at a rated... 

Material Capacity Suction pressure Suction temperature Discharge pressure Discharge temperature Compressor speed Single-cylinder, double-acting... 

Figure 14-4A. Oscillogram shows variation of current to a synchronous motor driving a reciprocating compressor, The compressor is two-cylinder, horizontal, double-acting, and operates at 257 rpm. Line A is the envelope of the current wave. Difference B-C is current variation. Value B-C divided by the rated full load current is the percentage of current variation. (Used by permission Oscarson, G. L. E-M Synchronizer, 200 SYN 52, p. 11. Dresser-Rand Company.)...

Part 1—One-cylinder, double-acting compressor, or two-cylinder, single-acting compressor. 

HA A single-stage double-acting compressor running at 3 Hz is used to compress air from 110 kN/irr and 382 K to 1150 kN/nr. If the internal diameter of the cylinder is 20 cm, the length of stroke 25 cm and the piston clearance 5%, calculate (a) the maximum capacity of the machine, referred to air at the initial temperature and pressure, ami power requirements under isentropic conditions. 

FIG. 10-68 Typical double-acting compressor piston and cylinder. 

Fig. 4.1-45. Double-acting compressor stage for 700 bar with a shrunk cylinder (NEUMAN ESSER). 1, Piston 2, Rod (crank side) 3, Tail rod 4/5, Shrunk compressor cylinder 6, Discharge 7, Suction.

Figure 29.1 is a simplified sketch of a cylinder of a reciprocating compressor. The cylinder is shown as a single-acting cylinder. Typically cylinders are double-acting, meaning that there are valves on both ends of the cylinder and that the piston is compressing gas, in turn, on both ends of the cylinder. 

A two-stage double-acting compressor with water cooled cylinder jackets and intercooler is shown in Figure 7.18(c). Selected dimensional and performance data are in Table 7.7. Drives may be with steam cylinders, turbines, gas engines or electrical motors. A specification form is included in Appendix B. Efficiency data are discussed in Section 7.6, Theory and Calculations of Gas Compression Temperature Rise, Compression Ratio, Volumetric Efficiency. 

---