System losses etc

[jsa]

Hello everyone,

I have been lurking around here for a few days reading what everyone has done to date and I must say this forum and your succeses are a credit to all involved. This information has saved me at least two bench redesigns.

I am embarking on my own flow bench build so that I can investigate a YB Cosworth cylinder head from an English Ford.

I have lashed out and bought 12 of the 491.3.707 motors with flow specs as per the attached chart.

Initially I had thoughts of Laminar Flow Elements or a Thermal Mass Flow Transducer for measuring flow, but it seems orifi and pitot's can be set up in a bench to work accurately. Always thought it odd to use measuring devices that were affected by the turbulence that should be generated by port flow.

I see orifi are commonly setup to use 6" or 13" max pressure loss for measuring flow. What about Pitot's, often stated as 2" insertion loss which I imagine is just the pitot and not the tube run, what pressure loss are people getting for the combined pitot/tube run ?

What amount of pressure drop are people experiencing between the fan and test piece, from flow path and measurement losses ?

I am having thoughts of configuring the motors so that I run up to all 12 in parrallel for large volumes at moderate test pressures and being able to change to a parrallel set of six in series with another parallel set of 6 for moderate volumes at high test pressures.

Do 2 vacuum motors in series actually double pressure at the flowrate of a single, or do they behave significantly different ?

Cheers

John

[Tony]

Welcome to the Forum John.

Total overall pressure drop will be the desired test pressure, plus whatever the design pressure drop is of your flow measurement device. The internal flow areas within the bench should be large enough not to create any significant additional parasitic pressure losses.

Yes, you can run blowers in series, and you just add the developed pressures, but I suggest you don't do it that way. Any of those blowers can easily develop at least forty to fifty inches pressure which is going to be about as much as you will ever require. In fact very high pressures can be dangerous in that they can burst or implode your bench if flow suddenly (accidentally) becomes blocked.

Just hook up all your blowers in parallel to get as much flow as you need to do the job.

Both orifice benches and pitot benches have advantages and disadvantages. The main advantage of an orifice bench is simplicity, and you can make it entirely yourself for virtually no cost. A pitot bench has many advantages, and most people are tending to build pitot benches these days. The only disadvantage is you will need to buy some electronics to get it going.

I have an orifice bench myself. But if I was starting out again completely from scratch, would probably go to pitot bench.

The decision is entirely up to you. You will find plenty of support here for either type of bench.

[jsa]

[Thomas Vaught]

Welcome John!

There are a couple of designs out there (Mouse's Tower of Power) that would work with a Pitot probe or with a Orifice arrangement.

Either way control of a given number of motors as far as air flow goes is fairly easy with Mouse's or 86 Rocco's air check valve designs.

In my mind, how much space you have is also a key part of the equation as is budget.

Keep us informed.

Tom V.

[Tony]

[jsa]

[jsa]