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Orifice Selection


The Scientific
Way

The Maximum Continuous Output Pressure and Maximum Output Flow are important in order to understand how many cutting heads you will be able to run with a pump. These numbers can be used in conjunction with the following “Flow Rate Through an Orifice” chart below to determine the number of cutting heads you can use.

Example 1: 50 HP Pump, 1 Cutting Head, 60,000 PSI, 1.1 GPM water output 

  1. If you were looking at the 50 HP pump, from the “Pump Specification” chart you would know that your pump puts out 1.1 gpm at 60,000 psi.

  2. You would look down under the “60” column (corresponding to the 60,000 psi pump) in the “Flow Rate” chart until you found a number equal to or less than 1.1. In this case, you would end up at the cell with 1.00.

  3. You would then follow that row across to the left to see the maximum size orifice you could use for single-head cutting. In this case, the cell shows that a 0.014” would be the maximum recommended orifice for one head at 60,000 psi.

  4. If you were in a tight spot where you only had a 0.015” orifice you might be able to use it by running the pump at 55,000 psi.


FLOW RATE (gpm)
THROUGH AN ORIFICE

    Orifice Diameter (inch)
    Pressure (psi) x 1000
    20 25 30 35 40 45 50 55 60
    0.003 0.03 0.03 0.03 0.04 0.04 0.04 0.04 0.04 0.05
    0.004 0.05 0.05 0.06 0.06 0.07 0.07 0.08 0.08 0.08
    0.005 0.07 0.08 0.09 0.1 0.1 0.11 0.12 0.12 0.13
    0.006 0.11 0.12 0.13 0.14 0.15 0.16 0.17 0.18 0.18
    0.007 0.15 0.16 0.18 0.19 0.2 0.22 0.23 0.24 0.25
    0.008 0.19 0.21 0.23 0.25 0.27 0.28 0.3 0.31 0.33
    0.009 0.24 0.27 0.29 0.32 0.34 0.36 0.38 0.4 0.41
    0.01 0.3 0.33 0.36 0.39 0.42 0.44 0.47 0.49 0.51
    0.011 0.36 0.4 0.44 0.47 0.51 0.54 0.57 0.59 0.62
    0.012 0.43 0.48 0.52 0.56 0.6 0.64 0.67 0.71 0.73
    0.013 0.5 0.56 0.61 0.66 0.71 0.75 0.79 0.83 0.86
    0.014 0.58 0.65 0.71 0.77 0.82 0.87 0.92 0.96 1
    0.015 0.66 0.74 0.81 0.88 0.94 1 1.05 1.1 1.14
    0.016 0.76 0.85 0.93 1 1.07 1.11 1.19 1.25 1.3
    0.017 0.85 0.95 1.05 1.13 1.21 1.28 1.35 1.41 1.47
    0.018 0.96 1.07 1.17 1.27 1.35 1.43 1.51 1.59 1.65
    0.019 1.07 1.19 1.31 1.41 1.51 1.6 1.68 1.77 1.84
    0.02 1.18 1.32 1.45 1.56 1.67 1.77 1.87 1.96 2.03
    0.021 1.3 1.46 1.59 1.72 1.84 1.95 2.06 2.16 2.24
    0.022 1.43 1.6 1.75 1.89 2.02 2.14 2.26 2.37 2.46


    You would be at the 1.1 gpm limitation of the pump. If there were any water leaks in your system between the pump and the cutting head, you would likely have a pump “over stroke” situation where the pump would try to cycle too fast attempting to create the required pressure. With modern pumps, there is no harm done if this happens. The pump is simply shut down to protect itself from damage and an error message is displayed for the operator.

    Running Two Cutting Heads

    Example 2: 50 HP Pump, 2 Cutting Heads, 60,000 PSI, 1.1 GPM water output

    If you wanted to run 2 cutting heads, then you would take the 1.1 gpm number, divide it by 2 for a maximum of 0.55 gpm per head. Look for the cell under 60 kpsi that has a number smaller than or equal to 0.55. In this case, under the “60” column you would end up in the 0.51 cell, meaning that one 0.010” orifice would put out 0.51 gpm. The maximum number of heads that you could run with the pump at 60 kpsi would be two (1.1 ÷ 2 = 0.55. 0.55 > 0.51 = OK).

     

    The Easy Way

    Since the pump design engineers have done most of the hard math already, most users need only refer to an “Orifice Selection Chart” similar to the following, which is usually supplied by the pump manufacturer. Here you would quickly see that for the 50 HP pump, you could use either one 0.014” orifice or two 0.010” orifices.

    ORIFICE SELECTION CHART FOR HYPERTHERM PUMP

    Max # Orifices 30 HP 50 HP 75 HP 100 HP 150 HP
    1 0.011 0.014 0.018 0.021 0.025
    2 0.007 0.01 0.012 0.014 0.018
    3 0.006 0.008 0.01 0.012 0.014
    4 0.005 0.007 0.009 0.01 0.012
    5 0.004 0.006 0.008 0.009 0.011
    6 0.004 0.005 0.007 0.008 0.01


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