My Bench..... taking ages!!!

[Mouse]

Rule of thumb in the electronics business is that you want your device to be rated for twice the max value it will see. So if you are pulling 10 amps, you want your controller to be rated for 20. Using 1000 watts, you want a 2000 watt controller. This gives you a lifetime saftey margine and accounts for peak values. But for specific controllers I don't know.

John

[jsmith]

Please checkout this speed controller



do you reckon it's 240v ac? It is supplied by an american company so I would have thought it would be 110...

[Brad]

I just sent this as a personal message when I meant to add a reply. I'm new and getting used to the system. Others can benefit from my comment if it makes sense. If it doesn't, one of the guru's, please straighten me out.
Where is the vacuum being sampled? One place is in the plenum on the vacuum side of the orifice. The other looks like it will have to be in the elbow portion of the plumbing. If the probe is placed in the high speed flow it can create erronious readings. If the plumbing is removed between the test hole and the orifice you could seal that portion of the box and have a second plenum. There will be leakage because the controls pass through; however, that can be measured and used as a correction factor.

[Brad]

Something you need to decide is how many motors. At light to medium loads on a vacuum motor, torque is proportioanl to the square of the current flow. If you double the current you get four times the tourque. Under heavy loads the field coils become saturated and the torque becomes equal to the current flow.
Load on a vacuum motor (a series motor) is the force needed to overcome the inertia of the air as it enters the fan and is spun. Increased resistance causes the motor to spin faster (hand over the nozzle of a vacuum cleaner) and the amperage DECREASES. If you want to regularly flow teast pieces in the 300CFM range, it may be more economical to use four motors rated at 110CFM each.
Another deal on motors...take them out of the housings. Also, lots of other motors.

[jsmith]

After reading some one else's ideas a few moths ago, I have re designed my bench.

Pic's to follow.

[jsmith]

1.

[jsmith]

2.

[jsmith]

Ok...

I decided I wanted to do away with the valves for regulating the pressure, so instead I have some router speed controls on order.

I am going to have 2 holes on my bench, 1 for inlet and 1 for exhaust. I have also done away with the complicated orifice assembly - I decided that is very over engineered and instead I am going to slide my orifice plates into a tight wooden sandwich.

I have also lengthened the pipework to hopefully get a smoother flow.

I have also redesigned the bench in such a way as that it will have a welded angle-iron frame which I will bolt my panels onto (using gasket tape to seal).

Currently working on the manometers - I have got stuck into the maths and have found that by altering my scale I can use small diameter wells and lose no accuracy.

[Brad]

Good morning, J., I have studied your new design at length and vacuum sampling still seems to be a problem. C'mon guys, help us out here. The focus of a flow bench design is aimed at getting accurate, repeatable vacuum depression readings. The first design has a nice plenum on the vacuum side of the orifice. That provides an area of relatively undisturbed air (lack thereof) for the topside of the manometer. But, on the bottomside, the sample seems to be taken from an area affected by high speed flow. I guess if the plumbing is large enough it can act like a plenum. In the second design the topside sample is taken directly from the vacuum chamber, which can be okay, but the bottomside is still taken from an area where it can be influenced by the air velocity. If the orifice is moved back toward the vacuum chamber it will provide a larger area (okay, volume) for the air to calm down a little. The plumbing still has to be fairly large.

[jsmith]

Thanks Brad,

I'm not 100% sure I follow what you are saying. I will be using an orifice plate (which slots between the 2 close wooden cross beams) to measure the pressure drop for the inclined manometer (this is standard orifice plate practice). The test pressure will be measured somewhere near the inlet hole.

Where do you think the problem will be?

[jsmith]

The red arrows show my intended position of the inclined manometer connections.

The blue arrow shows the intended position of my test pressure manometer connection.

[98-1074649673]

Why do you need the pipe? Other orifice bench designs don't use the pipe?

Then again I do the "pitot" thingey so I'm an outsider on this one

[Greg]

I agree with Bruce on this one, I think it would be better to use the area under the head adapter as a decent volume plenum. Wouldn't using a 90* bend just under the adapter direct the air at an angle against one side of the adapter bore?

I think a radiused entry on the side into a plenum area would provide a much smoother transition up through the hole in the top.

But then again, maybe I'm wrong!

An interesting test for anyone who has access to a Superflow 600 or MSD style bench using the angled board to mount the orifice plate is to measure a port then turn the head 90* and measure again then turn it 180* and measure again. You will find you get differing readings in each position due to the 45* change in direction the air has to make as it travels through the bench and the effect this has on the flow of air up through the adapter and port.

[98-1074649673]

Think you will find that this will have little effect on a SF style bench. They measure the difference between the outside air pressure of the bench and the pressure inside the bench before the orifice for differential pressure. The orifice is located at the very end of the airflow circuit through the bench and the holes are plugged or unplugged to allow more or less pressure to stay inside. Interesting to also note that heat inside this style of bench would also come into play I would think since the motors are located before the orifice. Anyone have any time on a bench like this? Hope this all makes sense?

[Brad]

This goes along with my post after the first design. Even in this design, if the plumbing is removed and the holes are left in there, the "orifice board" splits the bench into two plenums. One is between the test hole and the orifice and the other is between the orifice and the vacuum chamber.
I think the vacuum motors are mounted in the far back section.