减压孔板在室内给排水工程中，减压孔板可用于消除给水龙头和消火栓前的剩余水头，以保证水系统均衡供水，达到节水、节能的目的。
（1） 减压孔板孔径的计算：水流通过孔板式的水头损失，按式中计算：)10(242pa g H υξ= 1式式中 H ——水流通过孔板的水头损失值（Pa ）；ξ——孔板的局部阻力系数；υ——水流通过孔板后的流速（m/s ）；g ——重力加速度（m/s ）。
ξ值可从下列式中求得：ξ= 2式式中 D ——给水管道直径（mm ）；——孔板孔径（mm ）。
为简化计算，将各种不同管径及孔板孔径代入公式1式、2式，求得相应的H 值，所得计算结果列于表1.使用时，只要已知剩余水头及给水立管直径D ，九可从表中查的所需孔板孔径。
表1： 减压孔板的水头损失D （mm ） 3 4 5 6 7 8 9 10 11 12 13 15 20 25 32 40 50 81.03 262.3024.54 81.03 201.779.49 32.16 81.03 222.214.25 14.91 38.13 105.59 262.302.09 7.68 19.98 56.00 140.021.10 4.25 11.31 32.16 81.03 201.770.59 2.48 6.79 19.61 49.84 124.800.33 1.51 4.25 12.53 32.16 81.030.18 0.94 2.75 8.30 21.56 54.700.09 0.59 1.83 5.67 14.91 38.130.04 0.38 1.24 3.96 10.58 27.30D（mm）14 15 16 17 18 19 20 21 22 23 2420 25 32 40 50 70 80 100 0.240.862.837.6819.9881.03140.820.150.592.055.6714.9160.98105.590.090.421.514.5211.3146.6981.03201.770.050.291.123.238.7136.3063.13157.610.030.200.842.486.7928.5949.84124.800.010.140.631.925.3422.7839.83100.020.090.471.514.2518.3532.1681.030.060.361.183.4114.9126.2266.280.040.270.942.7512.2221.5654.700.020.200.752.2410.1017.8745.500.010.150.591.838.4014.9138.13D（mm）25 26 27 28 29 30 31 32 3332 40 50 70 80 100 125 150 0.110.471.517.0312.5332.1681.04170.850.080.381.245.9110.5827.3068.99145.600.060.301.035.008.9923.2959.07124.800.040.240.854.257.6019.9850.74107.540.020.190.713.636.5817.2343.8993.130.010.150.593.115.6714.9138.1481.030.120.502.674.9012.9733.2870.800.090.422.314.2511.3129.1062.110.070.351.993.709.9125.5954.70D（mm）34 35 36 37 38 39 40 41 4240 50 70 80 100 125 150 0.050.291.733.238.7122.5948.340.040.241.512.837.6820.0042.870.030.201.312.486.7917.7238.130.020.171.152.186.0115.7934.020.010.141.001.925.3414.1030.430.010.881.704.7612.6027.300.090.771.514.2511.3124.540.080.681.333.8010.1822.120.060.591.183.419.1619.90D（mm）43 44 45 46 47 48 49 50 5150 70 80 100 125 150 0.050.521.053.068.2818.090.040.460.942.757.4916.410.030.400.842.486.7814.910.020.360.752.246.1513.580.010.310.672.025.5912.380.010.280.581.835.1011.310.240.531.664.6610.350.210.471.514.259.490.190.421.373.908.71D（mm）52 53 54 55 56 57 58 59 6070 80 100 125 150 0.160.381.243.568.000.140.341.133.277.360.120.301.033.006.790.110.270.942.766.260.090.240.862.535.780.080.220.782.345.340.070.190.712.154.950.060.170.651.984.580.050.150.591.834.25D（mm）61 62 63 64 65 66 67 68 6970 80 100 125 150 0.040.140.541.693.950.030.120.501.563.670.030.110.451.453.410.020.090.421.343.170.020.080.381.242.950.010.070.351.152.750.010.060.321.072.570.050.290.992.400.050.270.922.24D（mm）70 71 72 73 74 75 76 77 7880 100 125 150 0.040.240.852.090.030.220.791.960.030.200.741.830.020.180.691.710.020.170.641.610.010.150.591.510.010.140.551.410.010.130.511.320.110.481.24D（mm）79 80 81 82 83 84 85 86 87100 125 150 0.100.451.170.090.411.100.080.391.030.080.360.970.070.330.910.060.310.860.050.290.800.050.270.760.040.250.71D（mm）88 89 90 91 92 93 94 95 96100 125 150 0.040.230.670.030.220.630.030.200.590.020.190.560.020.170.530.010.160.500.010.150.470.010.140.440.010.130.42D（mm）97 98 99 100 101 102 103 104 105125 150 0.120.390.110.370.100.350.090.330.090.310.080.290.070.270.070.260.060.24D（mm）106 107 108 109 110 111 112 113 114125 150 0.050.230.050.210.040.200.040.190.040.180.030.170.030.160.020.150.020.14D（mm）115 116 117 118 119 120 121 122 123125 1500.020.130.010.120.010.110.010.110.010.100.010.09 0.09 0.08注：表中给水管计算管径均采用公称直径表1中数据是假定水流通过孔板后的流速为1m/s时计算得出的，如实际流速与此不符，则应按式3进行修正，并安修正后的剩余水头查表。
3式式中——修正后的剩余水头（；υ——水流通过孔板后的实际流速（m/s）；H——设计剩余水头（【例】已知给水干管管径D=100mm，通过流量Q=40m³/h，设计剩余水头H=7m，如欲采用减压孔板消除此剩余水头，试计算减压孔板之孔径。
【解】已知D=100mm，H=7m得，υ=由3式得按D=100mm，，查表1得。