HSV for extra accuracy?

[FitheachSidhe]

Hello gents. Great product. Here's a simple perhaps stupid question: If the ERL pump's flow & pressure characteristics can be varied/controlled with a pwm sig, why the hsv? more precision? Also, given a fixed ratio, what would be the harm in letting the water run fulltime (ie: no cut in point) ? Just high water consumption? Thanks!

[Richard L]

Originally Posted by FitheachSidhe

Hello gents. Great product. Here's a simple perhaps stupid question: If the ERL pump's flow & pressure characteristics can be varied/controlled with a pwm sig, why the hsv? more precision? Also, given a fixed ratio, what would be the harm in letting the water run fulltime (ie: no cut in point) ? Just high water consumption? Thanks!

It is not a stupid question. It is perfectly true that the aquamist pump can be PWM driven - much easier than anything pump on the market.

There are a few factors that makes the 'diretcly pwm drive' un-precise. It is very simliar to varying the speed of a motor-driven pump and expect it to deliver flow linearly throught a restrictor. Speeding up the pump will only increase water pressure but not necesarily flow. Almost all WI system deliver water through a nozzle, any restricted orifice will create back-pressure as the flow inreases, it is the back-pressure that make the flowrate un-precise.

If the orifice of nozzle can be made variable, the flow will be more precise since the build up of the back-pressure is being relieved at high flow by opening up the restrictor.

The HSV is very simliar to a variable orifice. To some extent, it will also expecience backpressure since it has a nozzle in front of it. The only way this arrangement can give precise delivery is by matching a nozzle to give a specific flow range. Not far from using a different flow rate fuel injector.

More imortantly, since all automotive injections are controlled by PWM signal and it is much easier to define a "pre-scaled" dyamanic operating range - ie 0-100% duty cycle. One will know exactly at 0% duty cycle, the flow stops and at 100% duty cycle the system reaches full flow. Very easy for the user to log and map. Providing one can keep the system pressure constant.

If a system such as the aquamist's piston pump (stroke and cycle rate) or a motor-driven pump, they all exhibit the same problem when precision is concerned. It is a know fact that the aquamist pump has a limited flow compared to a motor-driven pump, but within it operating range it will deliver pretty accurate flow (0-300cc/min) compare to a motor driven pump that will deliver 0-3000cc/minute. This is of course both pump has being driven by a 0-100% PWM signal.

At 3000cc/minute, the motor driven pump will be very accurate at "open" flow (without restrictor). Other minor factors such as winding temperature increase (pump power loss) and speed of response in flow change due to inertia of the rotating mass.

The System 2d can be running full time since some one on this thread has just done that due to the freezing up of a manifold pressures switch. The consumption was not that much greater.