Capacity of the compressor should be determined with consideration of number of running unit, pipe fitting and also air leakage from the hose and pressure loss. Additionally, it is necessary to consider increasing number of air tool units in future and to be determined with sufficient allowance.

Generally if we need 1m³(Normal)/min(0.6MPa(Pe) at gauge) air, the compressor with 6-7kW capacity is required. How we can study according to using number of air tool unit? Air tool has different cases, such as sander for continuous work and impact wrench for discontinuous work. When you determine the capacity of compressor, you have to consider using number of air tool unit and also working condition with some additional coverage.

Therefore, necessary motive energy of compressor is calculated by the formula as mentioned below.H=(6 or 7)xQxKxF+A is the calculation formula.

H(kW) Necessary motive energy of compressor Q Air consumption of tool K Simultaneous running modulus F Operating modulus A Loss such as air leak

Table-1 Simultaneous running modulus (K) Total No. of unit Simultaneous running modulus 1-5 1.0 6-10 0.8 11-20 0.7 21-30 0.6 31-50 0.5 51-100 0.4 Overall air consumption of air tools is calculated by the formula, (average air consumption x using number of unit). However, all the fixed air tools seldom used at the same time. So, the capacity is determined according to simultaneous running modulus (as per Table-1) by using number of unit.

Table-2 Operating modulus(F) Operation condition Operating modulus Continuous work 1.0 Discontinuous work 0.5 Discontinuous work is a work which is continuously and not exceed a minute. In case of impact wrench, a work is only for 0.5-5 seconds, so it is discontinuous work.

Now, shall we try actual calculation? As the example, this is the case to use 2 units of KW-385GL (Air consumption = 0.72m³(Normal)/min.) and 3 units of KW-1600Spro (0.30m³(Normal)/min.) impact wrenches both for discontinuous work as well as use 2 units of PM-5 (0.25m³(Normal)/min.) wax polisher for continuous work. Also 1 set of 2-posts lift (0.20m³(Normal)/min.) and 5 units of air duster (0.08m³(Normal)/min.) are used as other equipment. In this case,

Using Model		Airconsumption	No. of unit	Operating modulus	Total m3(Normal)/min.
KW-385GL	Q1=	0.72x	2	x0.5	0.72
KW-1600Spro	Q2=	0.30x	3	x0.5	0.45
PM-5	Q3=	0.25x	2	x1.0	0.50
2-Posts Lift	Q4=	0.20x	1	x0.5	0.10
Air Duster	Q5=	0.08x	5	x0.5	0.20
Total	Q	-	13	-	1.97

Air consumption of air tools including operating modulus Q=1.97m³(Normal)/min. has been calculated. Total number of unit is 13 units. According to Table-1, simultaneous running modulus is K=0.7. Then, we substitute to the formula of H=(6-7)xQxKxF+A. It becomes H=(6-7)x1.97x0.7+A="8.3-9.7+A"kW. Loss "A" such as air leakage will be different depend on the line condition. So, we need the compressor which is equivalent to 11kW(15Ps) with some additional coverage.

We suggest you to take some additional coverage to the motive energy of compressor "H" with considering such as, capacity decreasing after long time use and increasing of using number of air tool unit in future.