Flow Rate Question

First, you need to know the roughness factor e the pipes. Then find the Reynolds number and the ratio e/D, D being the diameter of the pipes you are using. Next, based on the Reynolds number and the e/D ratio, refer to a Moody's diagram to find the friction factor f. This will account for the friction loss in the pipes.

Second, use the Energy equation to find the discharge pressure needed. To be safe, you can include a safety factor (say 1.2 or more )to account for clotting of the pipes and additional valves or flow devices. In this step, you will vary the lengths L from 25' to 200' as you will require. Based on the discharge pressure and flowrates, you can choose the pump needed.

Third, after finding the discharge pressure, you will need to check the NSPHA and NSPHR (net positive suction head available / required) of the chosen pump to see if it can match the requirements.

For dosing use a positive displacement pump. That way varying back pressure will have little effect on the volume of the material supplied as long as the pump is within its limits (such as peak pressure).

If the system that supplies the material has one pump and multiple tube runs with "T's" the dosing to each destination will vary depending on each individual run pressure losses. Therefor I hope each dose point can be supplied by one pump at a given time.

Hi,

You don't say what you're pumping and whether it is viscous. Do all the discharge points receive the 'brew' simultaneously or are they fed selectively. Imbalances in pressure losses in pipe length can be overcome by selecting larger bores for the longer runs etc. Likewise a distribution manifold with adjustable (needle)valves may be a more scientific option. The chosen pump is an issue and to avoid the pulsation from a piston type have you considered a 'peristaltic' version? They deliver a steady flow and provided the pressure requirement is not too high are good at transferring a wide range of fluids.

The application will be using peristaltic pumps. We use many sizes of peri pumps in the industries that we serve. Basically, what I was hoping to do was figure out what the discharge pressure would be through varying lengths of tube WITHOUT actually running the tube. If I could get "ballpark" numbers that were reliable, I could test just using a short tube, gage and ball valve to throttle back to the desired backpressure. As far as the distribution manifold and needle valves, yes we could do that, but that's more unnecessary hardware. I am using PWM to control the speed of the motor. The speed is user programmable on site and is setup during the calibration routine after all tubing and discharge devices have been installed.

Hi, AcesFull, thanks for the added info; looks like we are talking about similar types of application. I've found that when using these small bore plastic tubes that practice and theory are somewhat at variance, and the best solution comes down to a test using the actual tube left as a coil. If you buy the tube in say 100ft or 100yd reels you can easily set up the test before committing to the final installation

By trial and error I've also used a simple expedient of fitting an external screw clamp to the pipe needing added resistance, crude but effective and does not add more components to the line up.

Come back if you need more 'input'.

Yea, an actual test using a coil is what I would normally do. I was just not sure that a coiled section of tubing would be an actual and accuarate representation of how it might be installed in the field. Of course every installation will probably be different so test data aquired should only be used as a reference or guideline to get the user in the "ballpark" for a starting pump speed setting. They can then fine tune it through the calibration routine. Thanks for the input.

Testing through the coiled tube sounds like a fine idea to me. Your Peristaltic pump is a PD pump so is pretty immune to minor pipe resistance variations. All you really need to know is whether the pump tube will survive the back pressure at the desired flow, so this test would be perfectly adequate.

Hi AcesFull,

Thanks for the courtesy of the outcome; rarely do people finish off the thread properly so you never know what actually happened .

I wish you well with your venture. 'Bye for now.

Well just to close out the thread, I wanted to let you guys who gave me some feedback know that I went ahead and tested the full configuration as specified by the customer using their chemicals with all the desired flow control devices in place. Their products were not very viscous, worst case maybe something such as corn oil. After all the testing was completed, it has been verified that for this application there is little to no impact on flow thru the poly tubing tested at lengths up to 100'(spec changed yesterday). I would imagine that if the chemicals were a bit more viscous, this would not be the case. Either way, I was able to come up with a single pump/tube combination that covers the entire spread(min & max) of desired flow-rates for all chemicals that need to be used. Thanks to those who provided some feedback/info.