Flow rate and pipe size relationship

Flow Rate Vs. Pipe Size | Sciencing

flow rate and pipe size relationship

Pipe diameter calculation for known flow rate and velocity, in closed round pipe, applicable for liquids and gases. Hi, The answer is NO. if you use the equation Q = A*V where; Q = Flow Rate, A = Cross sectional area and V = Velocity. Since you have 2 unknown values, you. By understanding the relationship between flow rate and velocity, you'll The equation for pipe diameter is the square root of 4 times the flow.

If the pipe diameter is constant, the velocity will be constant and there will be no change in pressure due to a change in velocity. As an example, if an expansion fitting increases a 4 inch schedule 40 pipe to a 6 inch schedule 40 pipe, the inside diameter increases from 4.

If the flow rate through the expansion is gpm, the velocity goes from 9. The change in static pressure across the expansion due to the change in velocity is: In other words, pressure has increased by almost 0. Pressure Change due to Head Loss Since head loss is a reduction in the total energy of the fluid, it represents a reduction in the capability of the fluid to do work.

Head loss does not reduce the fluid velocity consider a constant diameter pipe with a constant mass flow rateand it will not be effect the elevation head of the fluid consider a horizontal pipe with no elevation change from inlet to outlet. Therefore, head loss will always act to reduce the pressure head, or static pressure, of the fluid.

flow rate and pipe size relationship

But is this figure true? Cross-check the result by working backwards. This adds up to 49, which is close enough to the expected figure of 49, This is supposed to be engineering, not physics.

Pipe diameter and flow rate calculator

Then the flow rate in the actual 4. And for the actual 7. Each pipe is carrying the same flow rate, as it should do. So the kitchen sink tap really will deliver 0.

flow rate and pipe size relationship

What if the pipes are too noisy? In a different design - perhaps one with with fatter pipes, or fewer elbows, or a larger head - the calculation might have predicted a much higher flow rate.

flow rate and pipe size relationship

In that case you would expect the pipes to be noisy when the water is running. To make them quieter, the water has to be slowed down, and this is actually very easy to do.


Any competent plumber installing a system will have included valves at strategic points, so that sections of the system can be isolated - when, for example, you need to change a tap washer. All you have to do is find the right valve and turn it down a bit. The extra resistance this adds will reduce the flow rate to a more sensible value.

Halving the flow rate would reduce the noise by a factor of four. Running a bath What is the flow rate out of the bath cold tap? This calculation is a bit more complicated, because it involves both the hot and cold water pipes in the two-storey house sketched above.

The approach is exactly the same: Think about the cold water first. The 22mm pipe from the tap is 3. It has an apparent length of: Similarly, the apparent length of the 28mm pipe is: Since there is no 15mm pipe involved in the runs to the bath, it seems silly to convert these lengths to their equivalent 15mm lengths, then add them together, then convert them back again to 22mm.

Instead, I'll simply convert the 28mm length to its equivalent 22mm value, using the figures in Table 6: Then the total equivalent length of 22mm is: The head is 3m, which corresponds to a pressure of: This is not terribly useful to know for a weight lifter but we will see how very useful it is for displacing fluids. Figure 26 You may be interested to know that foot-pounds of energy is equivalent to 1 calorie.

flow rate and pipe size relationship

The following figure shows how much energy is required to displace vertically one gallon of water. Figure 27 This next figure shows how much head is required to do the same job. Figure 28 If we use energy to describe how much work the pump needs to do to displace a volume of liquid we need to know the weight.

flow rate and pipe size relationship

If we use head, we only need to know the vertical distance of movement. This is very useful for fluids because pumping is a continuous process, usually when you pump you leave the pump turned on, you don't start and stop the pump for every pound of fluid displaced.

We are mainly interested in establishing a continuous flow rate. The other very useful aspect of using head is that the elevation difference or static head can be used as one part of the value of total head, the other part being friction head as shown in these next figure.

One shows the friction head on the discharge side and the other the friction head on the suction side. How much static head is required to pump water up from the ground floor to the second floor, or 15 feet up? Remember that you must also take into consideration the level of the water in the suction tank.

Therefore the total head will have to be at least 25 feet plus the friction head loss of the fluid moving through the pipes. Figure 29 How to determine friction head Friction head is the amount of energy loss due to friction of the fluid moving through pipes and fittings. It takes a force to move the fluid against friction, in the same way that a force is required to lift a weight. The force is exerted in the same direction as the moving liquid and energy is expended. In the same way that head was calculated to lift a certain weight, the friction head is calculated with the force required to overcome friction times the displacement pipe length divided by the weight of fluid displaced.

These calculations have been done for us and you can find the values for friction head loss in Table 1 for different pipe sizes and flow rates.

You need to have JavaScript enabled in order to access this site.

Table 1 Download a printer friendly version Imperial units or metric units. If the velocity is less, then the friction loss will be less and if the velocity is higher the loss will be greater than is shown in Table 1. This is why you normally see a bigger pipe size on the suction side of the pump than on the discharge.