One way valves

[Terry_Zakis]

You want to be sure that you don't run your motors with depression control, too low in speed, as the flow-through motors rely on the airflow for cooling. From my conversations with Ametek Engineering a while back, I belive 25% is the min flow you should run on a flow-through motor.

I posted an excel file on this forum a while back, which has performance curves for all of the Ametek motors I looked into, as well as performance notes from my conversations with Engineering support. Not sure what section it's in through!

Mouse, I like what you're doing with the check valves as well. Reading about someone else using flush valve flappers from a toilet was a great idea as well.

Best Regards,

Terry Terezakis

[84-1074663779]

Terry, that actually raises an interesting hypothesis.

When measuring very small flow numbers at low valve lifts, and normal full test pressure, there may only be perhaps one motor running, and several others turned off.

Allowing some air to bleed backwards through the unused motors may actually be beneficial. The one motor that is running will see higher internal airflow than the actual measured flow through the bench. That may be good for increased motor cooling.

As more motors are switched in, there will be less leakage, and with everything running flat out, one way valves will not be needed anyway.

My very first attempt ever at airflow experiments caused me to burn out a brand new leaf blower very quickly. Since then I have been very conscious of running motors at high back pressure where flow is almost completely restricted. A bit of a deliberate air bleed to assist motor cooling may actually be advantageous. Maybe one way valves are not such a good idea ?

[Mouse]

The problem with letting air pass through a vacuum motor that is not turned on is that it will spin backwards, quite fast sometimes. Turning on a motor that is spinning backwards may void the warranty, among other things.

John

[Terry_Zakis]

It's occurred to me that there are two ways to run the vacuum motors. All of the writeups that I've seen show the motors all flowing in parallel to one another. In this configuration, operation of a few motors will cause the in-operative ones to bleed back, and as Mouse pointed out they'll run counter-rotation. Starting them from this point will cause a surge of in-rush current that may cause pitting of the commutators.

The idea that I've been contemplating is the routing of the vacuum motors to produce flow in series. Perhaps with three stages of motors, say three banks of three motors. The inlet set of motors, with suction side to air source, would be operated with a variac in order to control speed. Discharge flow from this first set of motors would flow forwards through the next set of motors, and then on through the third set of motors to the unit under test. The banks of motors would be separated.

In this manner, with the first back on, the flow would be impeded more by rotating the two non-operational banks upstream. The total pressure ratio could become 3x's that across a standard motor, which could allow for testing under higher depression.

The tricky point would be to try and calculate what the flow requirements would be at the higher depression, and determine if each stage needed 2, 3, or 4 motors.

In this manner, there would be no need to check valves, and the successive banks would never rotate backwards.

Just a concept to consider.

Best Regards,

Terry Terezakis

[Thomas Vaught]

Terry makes a valid point.

Typically three motors or four motors always has enough cfm flow but not enough depression.

Two stage motors are simple two fans running on a common shaft.

Having a second or third motor behind the first might give more depression (like a 4 stage motor but you would have to be careful about the heat (lower cooling) on the second motor.

Superchargers have run staged boosting for years, why not staged suction?

Tom V.

[larrycavan]

[84-1074663779]

I am sure you are right, but accidents do happen.

If flow CAN be throttled right down to zero, sooner or later it will be. If the motors have even a small chance of bursting into flames inside a wooden bench, to me that would not be an acceptable risk. By the time you smelled the smoke it would be far too late.

It was raised as a hypothetical argument to raise peoples awareness of a possible situation. Personally I prefer to control motor speed electrically rather than run them flat out and throttle the flow.

Even better use a motor that does not depend totally on forced internal airflow for cooling. My bench uses a single 10Hp three phase motor and variable speed drive, so there is no possibility of a motor meltdown.

[Thomas Vaught]

I turn on the vacuum motors I use in pairs and use a by-pass system to always feed the motors cooling air. Each vacuum box for a pair of motors presently has a 3" manual slide valve sealing that box when it is not operational.

Tom V.

[larrycavan]

Tony,

The reverse flowing motors problem is definitely something to be overcome. I think there's merrit in John's one way valve concept. The operator would have to be asleep at the wheel to burn out a motor because of a restricted flow situation or be testing in an environment that is totally outside the realm of a multi vacuum motor bench.

I have never burned out a motor from such a situation and my bench was born in 93. I did have a motor failure from sparking though.

Motors in series is interesting but without a schematic of the configuraion my vote remains uncast. I picture a lot of inefficiency with that setup though.

The best way to overcome the flow reversal problem and in controlling the flow via an electronic setup is probably the way you're doing it with a single blower configuration. I do however reserve the option to check out John's new setup that Chad just invoked on his bench.

Larry

[Rick360]

I separated 2 of my 6 vac motors in a plywood chamber (they are tied to the same switch) and I put a couple of flap valves over holes in that chamber made from 2 or 3" square rubber sheet bolted above the holes to hang down in front and over the holes. I siliconed aluminum sheetmetal to the rubber on the back side to make it more rigid so as not to suck thru the hole. The rubber seals very well and the aluminum keeps it straight. It has been working this way for 15+ years without ever touching these flaps. Really very simple to make.

I either run just the 4 motors or turn all 6 on for higher flowing stuff. If flowing on lower lifts and the 2 with the flap valve are off, the motors are not spinning backward and will start right up and open the valves to flow more air when needed.

If you aren't running the motors you need to stop the reverse flow. They can get going pretty fast and why wear them out when you don't need to. Starting one up when spinning backward would be very hard on them for sure.

My bench has a bleed-off valve for pressure control so there will always be adequate flow for cooling.

Rick

[84-1074663779]

Larry,

I only raised this issue to make flow bench newbies aware of the potential motor cooling problem. I agree it would be difficult to do in practice, but if someone was totally unaware.....

[larrycavan]

Tony,

No problem. I apologize if there was an appearance of digging at you...Just making conversation...not intending anything more.

Best Regards,

Larry

[Nick]

I was interested in using toilet flappers for one way valves, so I bought some at Home Depo to experiment with. I put a 4in pvc coupling 4in long on the end of the motor and a piece of particle board with a 2in hole over that. The flapper was on the other side of the board. I do not think the flappers had enough strength to use. They pull inward so much it seems like they could get stuck in the hole. I have the 2 stage motors from surplus center, they claim 60in of water.

If I do use flappers I will try a piece of rubber glued to a piece of aluminum sheet. In my opinion toilet flappers are out, unless there are stronger ones out there that I did not see.

Just my 2 cents

Nick