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Backyard Flowbench

Started by _186sHK_ , Mar 21 2017 07:13 PM

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#1 _186sHK_

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Posted 21 March 2017 - 07:13 PM

A couple guys asked about my home made Flowbench in another thread, so here are the details on how I did it.

Here is a link to the site I got my info off for the basic principle and instructions on how to make it, http://www.musclecar...r-heads-part-3/.

Here are some photos of the bench with a little info, if anyone wants to know anything else (After reading the link) I'll try answer your questions when I can.

The main box is made of Plywood, and is 700L x 420W x 370H. After being screwed together, all joins were fiber glassed over and the whole box covered in resin.

It has 3 compartments, one directly below the bore fixture (left hand side of the box looking from front) that extends to the bottom of the box, and two chambers split horizontally on the right-hand side. The top chamber on the right-hand side houses two 1100watt vacuum cleaner motors, and the inlets to the motors are sealed up around holes on the bottom shelf of the top chamber so that they are pulling from the bottom chamber.

Each of the two right hand side chambers has a port that opens into the main chamber and a port to outside of the box, both of which can be blocked with o-ringed blanking plates.

When testing the inlet, the top right hand side chamber has the port into the main chamber blanked off and the port open to the outside of the box open, so the air comes into the main chamber from the head, down through the bore fixture, through the port in the lower right hand side chamber, up through the motors and out the top chambers external port.

When testing the exhaust the blanking plates are reversed so the air now enters from the outside of the box into the lower chamber, goes up through the motors and out the top right hand side chambers port into the main chamber then up through the bore fixture and head.

The manometer runs up and down the shelf support on the left-hand side of the bench and is plumbed to the main chamber, and reads from zero to forty inches of water.

The ball valve on the lower left hand side of the main chamber is to crack open before testing at very low cylinder head valve openings, down at 50 thou lift the vacuum can go over 40” and potentially suck all the water in the manometer through the bench, so you crack the valve, turn on the motors, wait for the water in the manometer to stabilize, then slowly close the ball valve, if it looks like it will go past 40 and the ball valve isn’t shut, you have to test at a higher valve lift.

When testing, the calibration plate on the top of the bench is completely blocked up, and you open the cylinder head valve in 50 thou increment’s, noting the vacuum

readings on the manometer at each stage.

These readings are then compared to the readings previously taken off the calibration plate. The holes in the calibration plate are sized for 5, 10, 20, 40, 80, and 160 cfm and by blocking and unblocking the holes in sequence and noting the reading on the manometer you get readings from 5 to 315 cfm in 5 cfm increments.

Because I don’t have any sort of voltage regulation yet, the vacuum the motors pull can vary depending on how much electrical load you have on in the rest of the house/garage, so after I test the head I will usually close the valve in the head and check the calibration plate tests the same as my reference readings, if not you can adjust the figures up or down as needed.

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#2 RallyRed

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Posted 21 March 2017 - 08:02 PM

I dont fully understand that..but its a work of art regardless.!

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#3 mick_in_oz

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Posted 22 March 2017 - 09:20 PM

Does this use a fluid reservoir? two of them, two manometers? one referenced to the other? if not, your bench will be very touchy with changes in weather, and more specifically density, a commercial bench has the two manometers reference to each other and this lets them track air changes so the results are repeatable, be it now, in an hr's time, or next week.

It may not be all that difficult to add the extra plumbing and referencing to make it lots more repeatable.

You don't need to regulate the voltage to make the motor vacuum consistent, you can simply have a point just before the vacuum to be able to bleed air into the system, this will let you adjust your test pressure, and if you had a test pressure manometer as well as an air flow manometer, there is no real need to adjust much, but you can also easily adjust to a certain pressure if that's what you're after.

I made a bench ages ago to do a carb and a bunch of other things, it can be amazing how much you can "find" with some plasticine and the smallest of changes, but also how much out of balance or variation there can be, and how easy it can be fifex with changing or biasing a radius towards or away from an opening.

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#4 _186sHK_

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Posted 24 March 2017 - 05:02 PM

I dont fully understand that..but its a work of art regardless.!

Thanks, dunno about work of art, but its fun to muck around on.

Does this use a fluid reservoir? two of them, two manometers? one referenced to the other? if not, your bench will be very touchy with changes in weather, and more specifically density, a commercial bench has the two manometers reference to each other and this lets them track air changes so the results are repeatable, be it now, in an hr's time, or next week.

It may not be all that difficult to add the extra plumbing and referencing to make it lots more repeatable.

You don't need to regulate the voltage to make the motor vacuum consistent, you can simply have a point just before the vacuum to be able to bleed air into the system, this will let you adjust your test pressure, and if you had a test pressure manometer as well as an air flow manometer, there is no real need to adjust much, but you can also easily adjust to a certain pressure if that's what you're after.

I made a bench ages ago to do a carb and a bunch of other things, it can be amazing how much you can "find" with some plasticine and the smallest of changes, but also how much out of balance or variation there can be, and how easy it can be fifex with changing or biasing a radius towards or away from an opening.

I'm not really sure what you are trying to say about a standard type benches manometers being referenced to each other?

It was my understanding on a standard bench (Superflow etc) the vertical manometer is used to set the test pressure, and the inclined manometer measures the pressure differential between

the calibration orifice(s) and the component you are testing.

I know an inclined manometer is more accurate than a vertical one due to there being more graduations for any given rise in the water, but could you please explain how any of this makes it more accurate with regard to the weather?

If you read the link posted you will see that mine is a floating depression bench, so does not require two manometers to get the flow figures.

And with regards to it being touchy with the weather conditions, the setup is in a lined and insulated attached garage, so not a huge temperature swing, and as long as I do a reference check with the calibration plate after a set of tests to make sure it lines up with the reference figures, this is not an issue.

It sounds like you may have had a bit of experience testing stuff yourself? If so you should read the link to get another perspective on floating vs fixed pressure benches,

It was written by Dave Vizzard, who I know a lot of people don't particularly rate, but when I read it it made a lot of sense to me, however the main reason I built the bench this way was it was cheep and easy with reasonable accuracy.

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#5 mick_in_oz

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Posted 24 March 2017 - 08:47 PM

Inclining a manometer only increases it accuracy as the fluid moves over a larger distance, when vertical 5" of H2O is 5" of fluid travel, when inclined 5"H2O may very well be 20" of fluid travel, depends on what angle you have the manometer set at, it changes the resolution of the manometer.

The point of a couple of manometers referenced to each other is so that weather does not affect it. Yes your bench may be in a great place all lined and insulated, but changes in air density will effect it lots, some days you may not notice the change much at all, others days it could be huge. Think changing air pressure from a High Pressure system, or a Low Pressure system, and the resultant changes in Relative Density, also called Density Altitude, I've see the RA change at the drags by some 3000' over as little as a few hours!

Referencing the manometers will mean you don't have to keep checking for error created due to weather, you simply read the manometers, write done the results, look up the corrections in the provided table and you're done.

I was more thinking, that it may not need much of a mod or addition to incorporate the changes to save you needing to constantly recheck with your reference plate to see if the changing weather has introduced errors.

My bench is home made, and cheap, but is plumbed like a commercial bench to account for the weather errors. It goes something like one reservoir is open to the atmosphere, the other reservoir is sealed, but the top is connected to the top of the opposite manometer. I'd really have to go and have a look but its in storage.

Dave Vizzard has a huge amount of stuff that is worth reading several times, some things may be out of date a little, but the fundamentals of airflow and pressure differentials never change.

There's a huge amount to be learned on a home made bench with a tub of plasticine and a roaring vacuum.

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#6 _186sHK_

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Posted 25 March 2017 - 09:15 AM

Inclining a manometer only increases it accuracy as the fluid moves over a larger distance, when vertical 5" of H2O is 5" of fluid travel, when inclined 5"H2O may very well be 20" of fluid travel, depends on what angle you have the manometer set at, it changes the resolution of the manometer.

The point of a couple of manometers referenced to each other is so that weather does not affect it. Yes your bench may be in a great place all lined and insulated, but changes in air density will effect it lots, some days you may not notice the change much at all, others days it could be huge. Think changing air pressure from a High Pressure system, or a Low Pressure system, and the resultant changes in Relative Density, also called Density Altitude, I've see the RA change at the drags by some 3000' over as little as a few hours!

Referencing the manometers will mean you don't have to keep checking for error created due to weather, you simply read the manometers, write done the results, look up the corrections in the provided table and you're done.

I was more thinking, that it may not need much of a mod or addition to incorporate the changes to save you needing to constantly recheck with your reference plate to see if the changing weather has introduced errors.

My bench is home made, and cheap, but is plumbed like a commercial bench to account for the weather errors. It goes something like one reservoir is open to the atmosphere, the other reservoir is sealed, but the top is connected to the top of the opposite manometer. I'd really have to go and have a look but its in storage.

Dave Vizzard has a huge amount of stuff that is worth reading several times, some things may be out of date a little, but the fundamentals of airflow and pressure differentials never change.

There's a huge amount to be learned on a home made bench with a tub of plasticine and a roaring vacuum.

Im still not seeing how the DA is affecting things as much as you are saying, I am well aware of how the DA changes effect things at Drags, I crewed on a car where we recorded all the variables before each run and adjusted the tune up to suit.

The air density at 40mtrs elevation above sea level, 10 degrees Celsius and 45% humidity is 1.234 kg/m3, change the temp to 30 degrees and the density drops to 1.147kg/m3, a change of .087kg/m3.

.087kg/m3 converted to inh2o is .0034 inches h2o, so on a vertical manometer 28" at 10 degrees would read 28.0034 at 30 (only taking into account the change in air temp not the water temp in the manometer) hardly a big diference.

One of the biggest variables is the specific gravity of the water in the manometer and how it changes with temp, if you isolate this variable the difference between a temp of 10 degrees and 30 degrees is .11 of an inch (28"h20 @ 10 degrees C would read 28.11" @ 30 degrees ) this difference would equate to less than 2cfm on my bench.

The other big variable is the actual gravity where you are, which varies depending on latitude, elevation and local topography. This will change the accuracy with regards to comparing figures in different locations (A 10° change in latitude at sea level will introduce approximately 0.1% error in reading)

Here is a good link to a site that explains the inaccuracies and how to correct them: https://www.calright.com/manometers

The only way I can see that you are getting a big change in readings with weather, is in the actual design of the bench, and the fact that a fixed pressure bench is measuring the differential between the calibration orifice and the test piece, not the overall vacuum reading that the floating bench does.

Edited by 186sHK, 25 March 2017 - 09:16 AM.