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Fluid Flow Control

Updated on July 10, 2012
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Choosing the Best Method for Paint Flow Control

This advice is from an engineering team that has been developing a high-tech painting tool with in-built colour blending capabilities. That means that different paint colours can be blended inside the machine creating brand new colours, gradients and exciting paint effects. In doing so we needed the paint flow to be very precise. We did not know when we started five years and four prototypes ago what would be best for our purposes, so we had to experiment with different valves until we found what worked best for us.

The many variables to be considered for various systems are: i) number of fluid streams; ii) combined or individual outflow of two or more streams; iii) continuous or intermittent flow of each stream; iv) volume of combined or individual outflow; v) geometry of inlet and outlet; vi) distance between inlet and outlet; vii) difference in elevation between inlet and outlet; viii) fluid pressure at inlet and outlet; ix) temperature of fluid at inlet and outlet; x) fluid viscosity; and xi) manual or computer control. Naturally, not all systems need to take into consideration all these variables.

As can be seen, systems can be complicated - increase in the number of variables involved, increases the degree of complication. Furthermore, the degree of accuracy required to control the flow of the fluid determines whether or not sophisticated computer software models of the system should be used.

The following illustrates the means of controlling fluid flow of relatively simple systems involving a few of the foregoing variables:

CASE 1 - A single continuous variable stream can be controlled by manual operation of a ball valve or if more accuracy is required, a needle valve is recommended.

CASE 2 - For instantaneous flow response, the valves used in CASE 1 can be preset for a given flow rate and a solenoid valve inserted in the stream to provide the ON/OFF function.

CASE 3 - For a timed response, operation of the solenoid valve used in CASE 2 can be actuated by a suitable timer to control its operation.

CASE 4 - For varying the flow during operations, the ball or needle valve can be operated manually, or an actuator can be used to change the valve setting.

And so it goes. Each additional feature requires the incorporation of additional controlling devices.

During the early stages of development of the Decoraxion, we used manually operated needle valves from Swagelock combined with manually controlled solenoid valves from ASCO to control multiple fluid streams with compressed air providing the driving force. When graduating to computer control, we investigated the use of actuators for valve operations. These proved to be too large and too heavy for our purposes and were forced to abandon their use.

Our latest Decoraxion prototype uses computer controlled self priming pumps to deliver precise volumes of fluid with fixed viscosity and specified output pressure.

The reader must realize that fluid control means and methods are determined by the required degree of accuracy of the value of the output parameters. Furthermore, the accuracy is also dependent upon the sensitivity of the output parameter monitoring device and the response speed of the feedback control system. For example, how fast does your hand react to adjust the hot and cold water taps in response to signals sent by your flesh that the shower water is too hot or too cold, and how long does the water take to travel up the pipe to the shower head?

Panaxion is an engineering development and design company located in Montreal, Canada. Founded by Frank McDonnell and Chris Frosztega, the company prides itself on integrating engineering with design and creativity.

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