Indicator card

Figure 12-16D illustrates the type of reciprocating compressor performance problems that can develop from various mechanical details. To maintain peak efficiency in a compressor cylinder, a pressure-time indicator card of the cylinder during operation can be quite helpful in pointing to a problem and its nature. ... 

Figure 12-17A. Combined indicator cards from a two-stage compressor showing how cylinder water jackets and intercooler help bring compression line nearer to isothermal. (Used and adapted by permission Miller, H. H. Power, 1944. McGraw-Hill, Inc., New York. All rights reserved.)...

Compression efficiency is the ratio of the work required to adiabatically compress a gas to the work actually done within the compressor cylinder as shown by indicator cards. Figures 12-12 and 12-16. The heat generated during compression adds to the work that must be done in the cylinder. Valves may vary from 50-95% efficient depending on cylinder design and the ratio of compression. Compression efficiency (or sometimes termed volumetric efficiency) is affected by several details of the systems ... 

Horsepower is the work done in a cylinder on the gas by the piston connected to the driver during the complete compression cycle. The theoretical horsepower is that required to isen-tropically (adiabatically) compress a gas through a specified pressure range. The indicated horsepower is the actual work of compression developed in the compressor cylinder(s) as determined from an indicator card. Brake horsepower (bhp) is the actual horsepower input at the crankshaft of the compressor drive. It does not include the losses in the driver itself, but is rather the actual net horsepower that the driver must deliver to the compressor crankshaft. 

A general appreciation of some of the effect of gas pulsation on the performance and impact on the compressor pulsation drums, their nozzles, the piping system, and the cylinder valve performance, as well as possible other effects in some unique systems or items of equipment, can be discovered by examining the cylinder performance using an indicator card. This examination (see Chapter 12) can reveal acceptable and unacceptable performance in terms of pressure variations within the cylinder as the piston passes through its cycle. Hicks presents a helpful analysis see Figures 13-3 and 13M. 

The power indicator cards of typical two- and four-cycle gas engines are compared with an accepted goal for a fuel-air cycle. The performance depends upon the type and composition of the fuel. Figure 14-35. 

The indicator card is useful in balancing the load per cylinder. The area of the card and the pressure-length scale are used to determine the horsepower. 

P = mean indicated pressure by measurement of the indicator card... 

Figure 14-35. Theoretical and actual gas engine indicator cards. (Used by permission Newcomb, W. K., 24 Conference, Oil and Gas Div.. American Society of Mechanical Engineers.)...

Positive Displacement and Carnot Cycle Use of Indicator Card... 

The output from the magnetic pickup and the output from the pressure transducer are connected to an oscilloscope. After a computer conversion of the data, the resulting pressure/volume plot is printed out. This plot is called an indicator card. The indicator card shown in Fig. 29.3 was generated from a 4000-hp natural-gas compressor in Hebron-ville, Texas. 

The solid line is the indicator-card plot. The dotted line is the Carnot or ideal compression work cycle which I have drawn myself. The piston position, shown on the horizontal axis, is proportional to the volume of gas inside the cylinder. 

Take a closer look at the discharge portion of the indicator card shown in Fig. 29.3. Note that the cylinder internal pressure rises well above the discharge-line pressure, before gas is pushed out of the cylinder and into the discharge line. This is a consequence on the spring tension of the discharge valves. 

In order to force these valves open, a certain amount of extra pressure in the cylinder is needed. The extra pressure overcomes the spring tension. Once the valve is open, gas flows out of the cylinder, into the discharge line, and the cylinder pressure falls. But, as shown on the indicator card, the discharge valve apparently opens and closes five times during one cycle. 

I could repeat the same story for the intake or suction valves. Leakage of the intake valves would appear as peaks on the compression portion of the cycle. Pulsation losses for the intake valves would appear as peaks on the indicator card during the suction or intake portion of the cycle. 

Other problems that can be identified by use of the indicator card are... 

The indicator card is the only real way to monitor reciprocating-com-pressor performance. Typically, the equipment and personnel to generate the card can be obtained from a local company specializing in this service. Often, the indicator card is referred to as a beta scan plot. 

Figure 2. Schematic representation of stages of Diesel combustion in relation to indicator card...

The course of combustion reactions during flammation has been studied 78) by the application of gas analysis techniques 40), by absorption spectra 76), by temperature measurements during combustion 95, 133-135), and by the analysis of indicator cards 25, 99,110.112). 

Steam (or other) shaft power is furnished as a part of the rental privilege in some (5ases. In the case of steam the average power demand is estimated by taking indicator cards at the prime mover, with and without the power load in question. Steam as such may be sold by steam meter or (for heating) on the basis of the cubic feet or square feet of space rented. 

The indicated horsepower, in the case of a steam pump HPt — HPw/Em> It i determined from indicator cards taken off the steam end. 

The apparent volumetric efficiency is the apparent volume of free air drawn in (as shown by the indicator card) divided by the volume of the piston displacement. This is the term that is commonly used in speaking of volumetric efficiency, and... 

The indicator card would be a true method of measuring the volumetric efficiency if the temperature of the air after being drawn into the cylinder were the same as that of the atmosphere, and if the pressure at the end of the suc-tion stroke were the same as that of the atmosphere. This is never the case. 

Once the network is finalized, the next step is to fill the assessment cards of all active PSFs. An indicative card for the PSF Level of Noise is presented as an example in Figure 9. 

Quality testing (filter paper test, indicator cards, etc.). 

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