Gate Valves

[DaveW]

I am building an orfice bench muck like the msd or superflow 600 and was wondering if gate valves will work instead of the bowls for the intake and exhaust? Dave

[84-1074663779]

A screw operated gate valve would work, but has one serious disadvantage. Control of airflow will be extremely non linear. The first couple of turns will gave a fairly rapid increase in flow, but going from say 60% open to 100% open will take a lot of turns without much change in airflow.

The "pudding basin" type of flow control valve works quite well in this regard because of it's shape.

Electronic speed control of the blower motor works even better.

[DaveW]

[Thomas Vaught]

DaveW,

On a Laminar Flow Bench design I did years ago I mounted two 3" opening valves side by side with a crossbar between the two push/pull rods.

On this Crossbar was a threaded nut.

The knob on the outside of the bench turned a threaded rod that moved the crossbar up and down.

To make the valves work correctly I had to make the plenum box shorter side to side so that the air could enter from the sides vs from the bottom.

The biggest advantage to the valves was that they were commercially available units used as toilet valves in Motorhomes. About $15.00 each.
They came with a very nice replacable seal on either side of the "tongue" valve. $ bolts mounted each valve to the plenum box.

At the time all I could find were 3" valves. I have been told that 4" valves are available.

I would rather use a Large Butterfly valve today
vs the "tongue" valves.

A SF Valve is made from aluminum and somewhat duplicates the mixing bowl design except it has a flat sealing surface on the end of the bowl lip. A piece of 1/8" plastic sheet with a hole (same diameter as the valve) allows SF to locate the valve opening perfectly compared to the centerline of the valve.

That is the way my next set of valves will be created.

Tom V.

[84-1074663779]

I agree with Tom, a large throttle butterfly would probably be better but it too would be quite non linear in operation. It could be greatly improved in action by linking it through a system of bell cranks.

Another wild idea that I have never actually tried, would be to fit a spring loaded arm with a roller follower on the end, onto the throttle shaft, and then use a snail cam to adjust the opening. With a bit of experimentation, fairly precise control of airflow over a wide flow range should be possible.

It is a lot of messing around, electronic speed control of the blower works far better than any throttling device. It vastly reduces the noise and power consumption and is a lot more convenient.

[bruce]

Here is an old pic of the gate valve I use on my pitot style flow bench. The threaded rod goes up to the top of the bench and has a round knob on it for adjusting the flow. I used a standard threaded rod, if I did it over again I'd use an acme screw for faster adjustment. I have not had a problem with biased flow past my averaging pitot tube.

[Thomas Vaught]

Bruce,

The rods I used for the dual deal had a piece of acme thread for the travel range. They don't give that stuff away though. It had fast adjustments though.

Tom V.

[larrycavan]

Just as a side not to this conversation....If you build it like the MSD / Mercdog design, the size of the valve determines how touchy the machine is to control valve opening rates.

A large [say 7"] can make the machine touchy. Also thread pitch plays into the picture as Bruce and Tom pointed out with Gate Valves.

I have 6" valves with .25/28 threaded rod attaching them to the knobs. This brings up something else that has never been discussed....."test pressure accuracy".

When I switched to digital flow measurements I could control test pressure down to the .01". Now that seems like an insignificant number but when you are .1 different between check lifts, comparing ports and wondering why a port is a CFM or two higher...test pressure accuracy can be the reason.

Larry C

[DaveW]

I dont use gate valves or the bowl design. Was just wondering how they would work because of the cost. I use throttle controls and made valves out of 6" PVC pipe with 1" holes drilled around the pipe. A 6" PVC Cap slides back and forth over the pipe which exposes the 1" holes or closes them off. I only played around with a 2.5 orfice and it seemed to control the pressure fine. When the valve is closed the cap is pulled tight against an oring which seals it completely. It seals so tight that I blew the back cover off which was caulked and had aleast 30 sheetrock screws in it. Definetly going to work on a releif valve.

Larry,
on one of your other post you talked about sealing the motors. I did this also with 6" PVC and a cap but on the end I glued a central vac wall cover plate with a 2" hole to the cap on the EX side which will only open if that motor is running. This lets me run only one motor (on int. side) at a time and not draw from the other motors for small orfices. If anybody wants pics I'll post them. Dave

[Mousehouse1]

Please post a few pictures Dave.

[DaveW]

[bruce]

PM sent on adding pics

[larrycavan]

[Nick]

Would not a cone shape like a long funnel be better than a mixing bowl shape? The idea is to make the valve open linearly. (Is that a word, humm)

I doubted if the motors would really turn backwards, I was wrong they go like crazy. The more depression the faster they go........

[larrycavan]