Re:
Hello Danno,
I am not a plumber, I am a Mechanical Engineering Technologist with design experience in fluid mechanics.
I believe you need a practical solution to your problem and without knowing the number and type of fittings, the pipe length and other variables it is not possible to calculate a flowrate.
You can rent or buy a flow meter that will measure the flow at the outlet to the dishwasher. There are available flowmeters made in many ranges. The problem is what range are you in? Further, the test needs to be done at the low pressure figure 20psig. You'll have to be able verify 20psig before doing the test to make it valid.
Here's a simplier solution. If you can find a container such as a beaker or bucket that is measured in the units you wish use. say gallons, and are able to redirect the flow at the dishwasher into it. you can measure the flow rate.
Simply, direct the flow into the bucket for 1 minute. or 1/2 min or some other convient period. Then, measure the water you've collect in that period. for your connection, use the same id as that of the dishwasher line and as short as practically possible. 1/2"pipe, I believe you said? Attaching a long garden hose won't do!
The math is simple. If you have say, 2 gal in a 1 min test then the flow rate is 2 gals per min.
Or 3/4 of a gal in a 1/2 min the you have 1.5 gal per min.
The best part of this test is that it is accurate. It will give you the exact flowrate at the outlet to that dishwasher at that time. Again, you need to verify that the pressure at the time of the test is 20 psig.
You can then write a report simply stating how you did the test at what pressure and the results.
Also, call Hobart and ask for a product or design engineer. Explain your problem. Ask him what minimum supply pressure is required for that specific unit in order for it to rinse streak free. He will most likely be more than happy to help and may be able to give you a minimum flow rate requirement to compare against your test. or maybe another solution. After all, Hobart dishwashers are his business. Engineers always go to the manufacturers when dealing with an equipment problem. You should too.
I believe the proper solution is to change the line and I assume you are looking for ammunition to support this. Hope this has helped.