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This page revised March 7, 2004
Valve Opening Fixtures
Repeatable valve opening is a must for flow testing. Over the years various valve opening fixtures have been designed. You can buy fixtures or fabricate your own. Most valve opening fixtures use one of three different methods.
The first method uses a dial indicator to measure the valve lift. Usually a screw pushes the end of the valve stem and the indicator measures the movement of the screw. The second method also uses a 1/4-20 screw to open the valve. A 20 tpi thread pitch produces .050 inch of lift for each full turn. With this method it is important to be able to accurately turn the screw EXACTLY a full turn.
The third method also uses a screw, but the screw does not open the valve. Instead it is turned until it just contacts the end of the valve. The valve is then opened by inserting spacers between the screw and the valve.
Head Adapters
Head adapters attach to the block surface of the head. They provide repeatable shrouding of the valves. Air is blown (for exhaust ports) or pulled (for intake ports) through the head adapter. Traditional flow benches have a work surface with a large hole on which a head adapter mounts. The head is then mounted on the top of the adapter. This type of head adapter can be used with Flow Quik by building a box with a large hole in the top on which you mount the adapter. We have named this box a "Test Plenum". The box should rest on legs so that you can bring the hose from the Flow Quick measuring unit into the bottom of the box directly below the hole in the top of the box. Do not bring the hose into the side of the box as this can result in uneven depression across the large hole. See the advice below on designing vacuum sources for recommendations regarding the sturdiness of the box.
Vacuum Sources
Flow Quik automatically compensates for variations in depression. "Depression" is the flow bench name for test vacuum (on intake tests) or pressure (on exhaust tests). As with any compensation it is better get the depression close to the standard value (usually 28 inches). Some heads (small block Chevy, for example) suffer from flow problems that do not appear until the air speed in the port passes a critical value. The only way to achieve the required air speed for properly test these ports, is to provide adequate depression at the higher lifts. When testing these kinds of heads your vacuum source should be able to provide about 28 inches at all lifts. This is beyond the capability of a single shop vacuum for the small block Chevy and similar size heads.
Two vacuums can be joined together with a Y fitting to produce a stronger vacuum source. Many Flow Quik users have also built their own vacuum source. Usually these boxes do not have the filters that a shop vacuum has. If you do this you should take extra care to clean intake ports before testing so that debris is not drawn into the motors.
Vacuum motors are readily available from Grainger , Hesco , and other supply houses. We recommend building a box to hold more motors than you plan to use. Screw a plywood cover over the ununsed motor mounting holes. This makes it easy to install more motors, if you find that you need more vacuum. The box should have two chambers with the motors mounted in the wall that divides the chambers. The motors will pull air from one chamber (creating a vacuum for testing intake ports), and push it into the other chamber (creating a pressure for testing exhaust ports).
The diagram shows an air supply with a flow direction control. The excess pressure bleed is needed to prevent over-ranging Flow Quik's depression sensor at low lifts. If it is constructed so as to provide fine control of the opening it can be used as a depression adjustment.
We sell a set of blueprints and fully illustrated instructions for building an air supply and a test plenum. The instructions include 50 color photos, a materials list, a sources list, and a cutting diagram. These are well worth purchasing since they will pay for themselves when they save from you one or two mistakes.
The fixed plates can be made from 3/4 inch thick melamine coated particle board. This material is used to make cheap shelves. It is available in various widths and 4 x 8 foot sheets at building supply stores. A good material for the moveable plate and spacer is 1/4 thick PVC sheet. Place a sheet of paper between the spacer and one of the fixed plates so that the moveable plate will have clearance to operate. A 1/4 inch dia. dowel pin makes a nice pivot. The rest of the unit can be constructed from the melamine board or 3/4 inch plywood. Reasonable sizes for the fixed plate are 18 x 18 inches with 4 inch holes.
When planning your installation consider which direction the air will blow when it exits the unit into the room. It's no fun chasing papers around the room after the air supply blows them off your workbench.
Keep in mind that 28 inches of water is approximately 1 psi. At 28 inches of depression a one square foot panel will have a force of 146 pounds on it. Therefore your box must be very sturdy. 3/4 inch plywood works well.
The standard 2 Inch Flow Quik measuring unit comes with 7 feet of the flexible spiral wrapped hose that appears in the photo between the measuring unit and the head. This hose fits nicely over OD of 2 inch diameter PVC pipe (2 3/8 inch OD). No clamps are needed to hold it in place. If you plan to use 2 inch pipe in your system avoid fittings that force the air to make sharp turns.
The large Flow Quik measuring unit uses 3 inch PVC pipe. There is no hose with the large unit. Use schedule 40 PVC pipe (standard drain pipe which you can purchase from a building supply house) and fittings to connect this unit.
The work surface on a standard flow bench has a 5 inch dia. hole in the center of a 4 bolt pattern. The standard thread size for the 4 bolts is 1/4 - 20, but some manufacturers now use 5/16.
1st Choice
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2nd Choice |
3rd Choice |
4th Choice
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Grainger Part No. 4M903
Hesco Part No. L-115923
Ametek Part No. 115923
120 VAC, 10.8 Max Amps
100 CFM at 28 inches
122 CFM thru 2 inch orifice
100.4 inch H2O in sealed chamber
Overall height: 6.2 inch
Diameter: 5.7 inch
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Grainger Part No. 2M424
Hesco Part No. L-116670-50
Ametek Part No. 116670-50
240 VAC, 4.0 Max Amps
80 CFM at 28 inches
102 CFM thru 2 inch orifice
87.8 inch H2O in sealed chamber
Overall height: 5.6 inch
Diameter: 5.7 inch
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Grainger Part No. 2M421
Hesco Part No. L-116669-50
Ametek Part No. 116669-50
120 VAC, 7.7 Max Amps
70 CFM at 28 inches
94 CFM thru 2 inch orifice
90.2 inch H2O in sealed chamber
Diameter: 5.7 inches
Overall height: 5.6 inches
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Grainger Part No. 2M194
Hesco Part No. L-116309-00
Ametek Part No. 116309-00
120 VAC, 6.8 Max Amps
57 CFM at 28 inches
112 CFM thru 2 inch orifice
63 inch H2O in sealed chamber
Diameter: 5.7 inches
Overall height: 4.5 inches |
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