Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 20 Air Compressors and Pumps

COMPRESSED AIR

Compressed air is used for:  Drilling rock  Driving piles  Operating hand tools  Pumping  Cleaning PUMP PAVING BREAKER

COMPRESSED AIR Things to consider: +Effect of altitude on capacity +Loss of air pressure in pipe and hose systems +Capacity factors

OVERVIEW Selecting the right air compressor depends on many factors. Ø Compressor capacity and operating pressure depend on the tools used. Ø Engine and compressor lose power and capacity as altitude increases and temperature rises.

AIR COMPRESSORS Compressors are rated based on the cubic feet of atmospheric air they take in each minute with a specific discharge pressure, usually 100 psi.

GAS LAW TERMS Absolute pressure of psi (14.7 psi common practice) and a temperature of 60 deg. F.  Standard conditions.

GAS LAW TERMS Gas-law equations are based on absolute temperature. k Absolute temperature is Fahrenheit plus 460°. k Capacity is the volume of air delivered by a compressor.

GAS LAW TERMS k Diversity factor is the ratio of the actual quantity of air required for all uses to the sum of the individual quantities for each use. TAMPER

EFFECT OF ALTITUDE The capacity of an air compressor is rated at a barometric pressure of 14.7 psi, (sea level). At higher altitudes the capacity of the compressor is reduced. This is a result of Boyle’s law.

ROBERT BOYLE Robert Boyle (January 25, December 30, 1691) was born in Ireland, the youngest of fourteen children. He chose a life of scientific inquiry and was educated in the finest possible manner of this day. He learned philosophy, religion, languages, mathematics, and most significantly the new physics of Bacon, Descartes, and Galileo.

BOYLE’S LAW Equ P 1 is the pressure of the free air when we are considering the use of a compressor.

BOYLE’S LAW P 1 (psi) changes with altitude:

EFFECT OF ALTITUDE Consider 100 cf of free air compressed to 100 psi gauge. Applying Boyle’s law. V 1 = 100 cfm P 1 = atmospheric pressure P 2 = atmospheric pressure + 100

EFFECT OF ALTITUDE Change in V 2 (cu ft) with altitude.

LOSS OF AIR PRESSURE in selecting the size of pipe or hose to use on a job. The loss of pressure due to friction as air flows through a pipe or hose must be considered

PRACTICAL EXERCISE What will be the pressure at the end of a compressed air pipeline used to transmit 3,000 cfm of free air. Hose Pipe

PRACTICAL EXERCISE The initial pressure is 100-psi gauge and the 6 inch pipe w/screw fittings is composed of the following: 1,400 feet of pipe 3 gate valves 1 angle valve 2 long-radius ell’s

STEP 1: EQUIVALENT LENGTH OF PIPE Table 20.2 : 6 inch pipe Pipe 1,400.0 ft Gate valve 3 X 3.5 = 10.5 Angle valve 1 X 84.1 = 84.1 Long-rad. ell 2 X 6.1 = 12.2 Total = ft

STEP 2: PRESSURE LOSS per 1,000 ft Table 20.1: Free air: 3,000 cfm 6 in. pipe 2.26 psi per 1,000 ft of pipe

STEP 3: PRESSURE LOSS for EQUIVALENT LENGTH

STEP 4: PRESSURE at END of PIPELINE Initial pressure psi Pressure loss Pressure at end 96.6 psi

PRACTICAL EXERCISE No. 2 The air at the end of the pipeline is delivered to the tools through 60 ft of 1 1/2 in. hose. Each tool requires 140 cfm of air. What is the pressure at the tool?

STEP 1, PRESSURE DROP from TABLE Use Table 20.5, to determine the pressure drop caused by the hose. Volume of air: 140 cfm Size hose: 11/2 in. Pressure at line: 96.6 psi

STEP 1, PRESSURE DROP from TABLE Volume of air: 140 cfm Size hose: 1 1/2 in. Pressure at line: 96.6 psi For both a 90 and 100 psi at line pressure, the loss is 0.2 psi per 50 ft.

STEP 2, PRESSURE DROP ADJUSTED for HOSE LENGTH 60 ft of 1 1/2 in. hose

STEP 3: PRESSURE at END of HOSE Pressure at pipe psi Hose pressure loss Pressure at tool psi If the tool required an operating pressure of 100 psi there would be a 4% loss in efficiency.

PE No. 2; w/ 1 in. hose Consider if 1 in. hose was used instead of the 1 1/2 in. what would be the pressure at the tool?

STEP 1, PRESSURE DROP from TABLE Volume of air: 140 cfm Size hose: 1 in. Pressure at line: 96.6 psi Table 90 psi, 2.4 psi 100 psi, 2.1 psi drop/50ft

STEP 1, PRESSURE DROP from TABLE Pressure at line: psi, 2.4 psi 100 psi, 2.1 psi drop/50ft 10 psi 0.3 psi X = 0.198

STEP 1, PRESSURE DROP from TABLE Pressure at line: psi, 2.4 psi 100 psi, 2.1 psi drop/50ft X = = psi drop/50ft

STEP 2, PRESSURE DROP ADJUSTED for HOSE LENGTH 60 ft of 1 in. hose

STEP 3: PRESSURE at END of HOSE Pressure at pipe psi Hose pressure loss Pressure at tool psi Pressure at tool 1 in. hose psi Pressure at tool 1 1/2 in. hose psi

CAPACITY FACTORS All tools will not be operating at the same time. Therefore capacity (diversity) factors are used in planning systems.

PRACTICAL EXERCISE Seven 80 lb paving breakers will be used on a job. If it is expected that no more than 5 drifters will be consuming air at a given moment, the compressor should be sized to provide how many cfm?

STEP 1, AIR per TOOL 80 lb paving breakers Check the manufacture's data sheet. Table 20.6 gives representative values for the quantities of compressed air required.

STEP 1, AIR per TOOL 80 lb paving breakers Table 20.6, page cfm each Without drill specific data we will use 65 cfm

STEP 2, ADJUSTED for NUMBER in OPERATION 65  5 = 325 cfm Therefore a compressor capacity greater than 325 cfm should be provided.

COMPRESSOR SELECTION 1.Tools or equipment to be used. 2.Air (cfm) requirement of each. 3.Pressure (gpsi) requirement for each 4.Piping and hose lengths

COMPRESSOR SELECTION 5.Capacity factor. 6.Theoretical compressor size. 7.Economical compressor available, that exceeds theoretical requirement and provides flexibility.

COMPRESSORS