coolingmist

I apologize for the length of this thread up front. I cant seem to say what I want in just a few sentences. Please hit the back button if this bores you

There have been alot of threads lately about demand switch shurflo pumps vs shurflo pumps with bypass switches.

The advantage of the bypass pump is that it does not pulse, it gives smooth consistent flow, the disadvantage is that its only around 120 psi at max. The advantage of the Demand switch pump is that the pressure is far superior at 150 psi, but the flow can be inconsisent and pulsing can cause a disruption of flow and at a certain point a progressive style controller would no longer be progressive. I just finished writing a utility for our Vari-Cool customers to stop pump pulsing. When we designed vari-cool we built alot of features. It was designed with the idea when new technologies or new challenges arrive we can adapt new technology or a different product with vari-cool.

Through our free laptop sw our customer has rull controll over the Start dutycycle, full dutycycle, curve, tuning ****, min psi, max psi, etc of vari-cool. Most of you are aware of that, but what you may not be aware is that vari-cool was designed so that we can set the PWM resolution through the controller just by changing a few values in the software and writing to the flash.

The "demand switch" pump is a great example. I will do my best to explain how this demand switch can affect progressive style system. This part does not just affect Vari-Cool, but all progressive controllers attached to a Demand switch style pump which I am fairly certain is all of them.

The size of the nozzle is what will determine the dutycycle that the pump will shut off. The smaller the nozzle the lower the dutycyle the pump will shut off and the less range your progressive system will have. The larger the nozzle the more range and higher dutycycle before the pump shuts off. During the shut off process you will still be flowing but the flow rate will be lowering. Often this happens so fast that the pump pulses rapidly. If you have large enough nozzles your pump would never pulse, but for most of us the pump will pulse.

ok, bear with me for a moment. Now lets look at a progressive controller hooked up to a demand switch, any will do. Lets say that a 6 GPH nozzle (M5) causes the pump to shut off at 75% dutycycle. In that same example lets say that your Min setting is 1 and your max setting is 20. Lets assume that 75% dutycycle hits around 15 PSI. That means you will hit your full flow potential at 15 psi and you have a "dead band" from 15 to 20. In otherwords, your system will not be progressive after 15 psi and after 15 psi your flow will be erratic, pulsing back and forth with no more "progressive" feature.

The above example would be true for any progressive controller that is using a demand type pump. With Vari-Cool you have the ability to change the resolution of the controller to get rid of the pulsing and change the curve. What this will do is give you less flow down low where you dont need it and more flow up high and make it completely progressive throughout the entire boost range. The other nice feature is that it will give you a full 150 PSI (30 more PSI than the bypass pump) for better atomization and range.

In the example above we had the Min at 1, Max at 20, the pump would hit 150 psi by 75% dutycycle which would happen at 15 psi. By setting the max dutycycle to around 74% that would mean at 15 psi you may have 60% dutycyle and will continue to be progressive until the max dutycycle is reached at 20 psi. This software will be on our website shortly for our customers to download free. Its important to note that you can set these features in all Vari-Cool controllers that were ever sold, but only version 1.03 and 1.04 + can use this utility. That would be all vari-cools that have a brass pressure port and most that were sold after Oct 2006. The utility is nice because you just hook up a few wires, press a button and it calibrates it for you. Those of you that have our older controller will have to do find out what the dutycycle is where it starts to pulse and enter those values in manually through the free laptop software.



Let me know if anyone has questions.

radkins

Have you tried using a typical hammer effect eliminator that they sell for home pluming? Although I doubt it would work at such a high pressure.

coolingmist

You would not want one of those, by matching the PWM resolution of the controller to the pump you will get better range and resolution. To use any type of accumulator would be counter productive.

CM