Calculating Water Flow Using Ohm's Law - Index

TABLE OF CONTENTS - OHM'S LAW FOR FLUIDS

NOTE - Ohm's Law is not as useful working with closed loops which have individual pressure sources

EXAMPLE 2a Calculate flow in gpm for one 2 inch hose feeding two smaller handlines
STEP 1 Add the hose resistance and the nozzle resistance together to give an equivlent
STEP 2 Add the hose resistance and the nozzle resistance together to give an equivalent
STEP 3 Convert the two equivalent resistances from Step 1 and Step 2 (they are in )
STEP 4 Add the resistance calculated in Step 3 to the resistance of the 2 inch hose
STEP 5 Solve for flow

EXAMPLE 2b Calculate the flow in in the individual hoses.
SOLUTION We have just found the total flow (219.8 gpm) and we know that all FLOW DIVIDES between two parallel resistances based on how the resistances

EXAMPLE 2c Calculate the pressure at each nozzle and at the wye.
SOLUTION We're going to do this three different ways, just for practice. None of them are hard.
THE EASIEST WAY - Use EK's Friction Loss and Nozzle Flow Calculator. We already know the ...
Chart Step 1 - Find the pressure at the wye. Draw a line between the 2 inch hose mark and ...
Chart Step 2 - Find the pressure at the 5/8 smoothbore, which we already know is flowing ...
Chart Step 3 - Find the pressure at the 7/8 smoothbore, which we already know is flowing ...
NOW - Let's do it with numbers. We know the flow, so it's easy to work out the pressures.
Numbers Step 1 - Find the pressure at the wye. The pressure drop in the 2 inch hose equals ...
Numbers Step 2 - Find the pressure at the 7/8 nozzle. The pressure outside the nozzle, in the ...
Numbers Step 3 - Find the pressure at the 5/8 nozzle. The pressure outside the nozzle, in the ...
The nozzle pressures could also be found by calculating the friction losses in the hoses ...
FINALLY - Let's find the pressure at the wye and at the two nozzles without using the flow.
Ohm's Law Step 1 - Find the pressure at the wye. We need 3 things: the pump pressure, ...

How Pressure Divides (General Case)
In fact, this same thing works for any number of resistances in series - the pressure across ...
The interesting point is that you don't need to know the flow to see how the pressure divides.
Next, we'll work out nozzle pressures, using the pressure at the wye as our "total pressure" ...

Talking about Power (Without Numbers)
POWER - Power is the rate at which energy is generated or used, in terms of Energy per Unit ...
Three common ways to describe Power are foot-pounds per second, Horsepower and Watts.
HP = gpm x psi / 1714.55
This is the basic formula - if you know the gpm and the psi, just go ahead ...
Let's look at crimps in a hoseline. Do they matter?
For a given amount of flow, the pump must supply a certain amount ...
But, and this is important, when the pump pressure goes up 20 percent, then for the same flow, the horsepower also goes up 20 percent.

HORSEPOWER CALCULATIONS USING FLUID WATTS.
THE BASICS
For example, a pump which adds 90 psi to a flow of 125 gpm requires 6.56 horsepower to ...
The HP formula given above is basic, but it's not always the easiest formula to use.
The trick is to work with fluid watts, where 1 Fluid Watt equals 1 gpm pressurized by 1 psi ...
1714.55 fluid watts equals one horsepower
Other Formulas
Fluid Watts = Gpm x Psi

THE VIRTUAL NOZZLE and Bernoulli's Equation
The Frictionless Pump and Hose
TRASH PUMP Part 1, with warts - something is missing. What is it?
In our model, the pump is the pressure head, and the virtual nozzle is the size of the hole.
The value of the virtual nozzle depends only on its diameter, and is the same as the resistance ...
Virtual Nozzle Resistance Values for 3 Common Hose Sizes

Portable Pond Fill Times with and without a Hose Crimp
Power Calculations for the Pond Fill Example including at the Virtual Nozzle ...

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