Not sure if i'm in the correct category but I need assistance with two things:

I'm looking for a way to either start/stop airflow via a valve of some sort in a schedule 40 4" diameter pipe or some kind of valve that will bleed off the pressure (low pressure down to 140" of water) in the pipe when opened. The start/stop method is preferred but i believe bleeding the pressure off would work as well. I also need a way to electrically control the opening/closing of the valves so the time is the same or repeatable each time. I'd like to be able to open/close it through several cycles and i'm looking for a way to do this as fast as possible. I have a four channel pc based digital oscilloscope that i plan on using to measure the open/closed times and I'm not really sure the best way to do this.

I've found some electronically controlled in-line butterfly valves but all the ones i could find appeared to be incredibly slow. I've also looked at some manual or mechanical vacuum relief valves but obviously they're not electrically controlled.

Any help or suggestions would be appreciated.

 

If you are just "bleeding off" air pressure, could you not use a small solenoid valve, with 1/8" NPT ports?

Or do you need a full-bore open 4" valve?
Large fast valves this big are going to be crazy expensive.

 

If you are just "bleeding off" air pressure, could you not use a small solenoid valve, with 1/8" NPT ports?

Or do you need a full-bore open 4" valve?
Large fast valves this big are going to be crazy expensive.

I think i probably could. It's just a matter of how to control it and how fast i can control it because the faster the better. I would just have to experiment on what size it would take to quickly bleed off 140" of water depression in a 4" pipe to atmospheric, or close to atmospheric, as quickly as possible. Maybe i would have to control, for ex, two relief valves instead of one to get the job done but i don't know yet. The main thing i need at the moment is how to do it and yes a simple, hopefully not to expensive, method would be preferable. I don't have enough back ground to figure this out myself.

 

Can't offer much based on the limited amount of information provided.

Can you define the problem more clearly?

What is the system for?
How fast is "quickly as possible"?
What is the volume of gas to be vented?

 

Not sure I follow your purpose and desire. What comes to mind is a sprinkler control valve. Opens and closes pretty quick. As for controlling the flow rate, a second, hand adjusted valve could be employed.

140" of water ? ? ? 11 feet 8 inches ? ? ? That equals 5.059 PSI.

One foot of water in a pipe exerts 0.4337 PSI. Multiply that by the feet of elevation and you get your figure. The diameter of the pipe does not play in factoring in the pressure. A quarter inch pipe standing 11.67 feet high will have the same PSI at the bottom as a 4 inch pipe. The whole rig will definitely weigh more, but the pressure at the bottom will still be the same.

 

If you have a four inch diameter pipe standing 11 feet 8 inches then you have a total volume of 1758.4 cubic inches of water. There are 231 cu in of water in one gallon. That's 7.6 gallons (roughly). Do you want to drain off the 7 gallons? Or just the pressure? If just the pressure, remember, water has weight by elevation of 0.4337 PSI. To drop that to atmospheric, you have to drain the entire pipe.

This is why I say I'm not sure I follow your intended question.

[edit] Looks like I took off with the "Water" part of your question. Still, the PSI should be the same. Bleeding off 5.06 PSI through a 1/8 inch or 1/4 inch valve shouldn't be difficult to achieve. As long as we know what "As Fast As Possible" means. The lower the air pressure the slower the venting. So a quarter inch valve might not serve AFAP.

You mentioned 140 inches of water, so how does air pressure figure in? A picture paints a thousand words, so if you could give a rough diagram of what you have to work with would be of help. As for the rest of my answers, obviously they were with the venting of water. But I HAVE seen sprinkler valves used as air pressure rocket launchers; so they must open pretty rapidly.

 

Another water valve that comes to mind is that of a washing machine solenoid valve. They operate on 120 VAC. Old dishwashers also have those valves. I believe I even have a few in my garage right now. The thing about the sprinkler valve is that they operate on 24 VAC. They MIGHT even work on 24 volts DC, but that might generate excessive heat. Perhaps 12 volts DC may open them, but you'd have to experiment.

 

So you are looking at a 4" diameter pipe (schedule 40) with 140" of water column pressure or about 5 PSI (low pressure). You want speed and the ability to bleed pressure on the downstream side when the valve (supply side) is closed. In order to have the bleed function you want to look at 3 way valves and for speed a solenoid operated valve. Good luck on that as most large diameter valves I worked with were gate type and operated pneumatically.

On a 3 way valve you have 3 pipe connections and two orifices. when either orifice is open the other is closed and vice versa. Common use is to apply pressure and allow exhaust (bleed). You can also use a standard 2 way valve and add another valve for your bleed function but I would be looking at a 3 way valve all in one nice package.

If you can use PVC pipe schedule 40 the cost will come down but even PVC valves with a 4" body are expensive. Pressure with 140" of WC (Water Column) is not a problem. The problem you will likely run into is while the pressure is low, very low, you still have pipe with a 4" ID which is a large ID for most of the faster valve body types.

A more detailed, as suggested, goal may help you get better solutions I am just assuming the medium is low pressure water, possibly used in irrigation or similar. What is the existing pipe composition? Will PVC work for your application?

Ron

 

So you are looking at a 4" diameter pipe (schedule 40) with 140" of water column pressure or about 5 PSI (low pressure). You want speed and the ability to bleed pressure on the downstream side when the valve (supply side) is closed. In order to have the bleed function you want to look at 3 way valves and for speed a solenoid operated valve. Good luck on that as most large diameter valves I worked with were gate type and operated pneumatically.

On a 3 way valve you have 3 pipe connections and two orifices. when either orifice is open the other is closed and vice versa. Common use is to apply pressure and allow exhaust (bleed). You can also use a standard 2 way valve and add another valve for your bleed function but I would be looking at a 3 way valve all in one nice package.

If you can use PVC pipe schedule 40 the cost will come down but even PVC valves with a 4" body are expensive. Pressure with 140" of WC (Water Column) is not a problem. The problem you will likely run into is while the pressure is low, very low, you still have pipe with a 4" ID which is a large ID for most of the faster valve body types.

A more detailed, as suggested, goal may help you get better solutions I am just assuming the medium is low pressure water, possibly used in irrigation or similar. What is the existing pipe composition? Will PVC work for your application?

Ron

 

Sorry for the delay and thanks for the replies. I'm building an airflow bench for automotive purposes. My goal is to simulate the interruption of airflow by the valves as best as i can. I was originally going to use some sort of inline valve as previously mentioned but i think i can use a bleed valve instead. It wouldn't be quite the same as directly starting/stopping the airflow but i'm thinking that bleeding off the air pressure would somewhat effectively stop the airflow because basically you're changing (or bleeding) the pressure which would effectively stop the airflow, or at least enough for me to do what i want to do....I think. Short of having a test engine driven by an electric motor or a bunch of money to do it a different way i think this will give me something i can work with.

It's not about the pressure in a 4" pipe, per say, it's about having a large enough bleed to displace the volume of air going through the pipe to in turn raise the pressure back towards atmospheric.

I will have multiple vacuum motors, starting out with four then moving up to twelve at some point. Each motor is rated at 120 cfm and 140" water. My bench is quite a bit different than the industry standard so i'm in unfamiliar territory here.

 

Lets say i go with a normally closed solenoid valve. I drill a hole in the side of the pvc pipe and mount the solenoid to it so that it would vent the pressure external to the pipe. What would be the best or simplest way to control the valve? I need something that would cycle it open/closed when activated. Preferable something that i could adjust if desired.

 

I'm wondering at this point if it would be easier to take a blast gate valve, the kind you see in shop vac's and build your own solenoid to open and close it. Like this:

https://www.amazon.com/POWERTEC-70135-4-Inch-Aluminum-Collector/dp/B00LPPF0S6/ref=asc_df_B00LPPF0S6/?tag=bingshoppinga-20&linkCode=df0&hvadid={creative}&hvpos={adposition}&hvnetw=o&hvrand={random}&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl={devicemodel}&hvlocint=&hvlocphy=&hvtargid=pla-4584001418708388&psc=1

Otherwise, I'm still having trouble understanding exactly what it is you want to do. 140" water ? ? ? Where does water come in with an air flow bench?

 

That's an interesting idea, i'll definitely spend some time thinking about that.

 

Keep in mind it doesn't create a perfect seal. It doesn't stop all air flow. As far as shop vac's go, you depend on a higher volume of air flow to carry dust away to the vac. Nobody cares if there's a slight leak in one of those valves. If you need an absolute seal then this is not the valve for you.

As far as creating your own solenoid, could be a DC motor and gear that can swing the gate open and closed, hopefully fast enough for your application. ME? I don't see speed being that critical. But then again, I don't fully understand what it is you're doing.

 

I'm trying to duplicate the starting and stopping of airflow that occurs inside a four stroke engine when the valves open and close. Obviously i can't do it in the same time frame but i will do the best i can.

 

Four cylinder engine. Always one cylinder in the "Intake" stroke. If viewed as a wave form it would look like a full wave rectified trace. And no, you're not going to come anywhere near the start and stop strokes of an engine. Perhaps for a six or eight cylinder engine there may be a continuous airflow of varying degree; but why would you need that?

What about a throttle body from a junk yard? That has a butterfly valve and can be set up to open and close rather quickly.

And if you NEED to have that particular sort of airflow then just make your own butterfly inside the four inch PVC. Mount it on a shaft and to a motor. That way it is constantly opening and closing. Depending on how fast you run the motor / butterfly you'll get pretty close to what you want. Forget about gates and bleeders. If you want a continuous air flow of some small degree when the valve is effectively closed you can drill small holes in it until you achieve the desired result.

 

Otherwise, I'm still having trouble understanding exactly what it is you want to do. 140" water ? ? ? Where does water come in with an air flow bench?

It should be WC (like reloadron said) a measurement of gas pressure, like when they talk about "inches of mercury". Inches of mercury is for higher pressures than inches of water. Kind of a more scientific way than PSI.

 

@ Learner1968 have you seen this - http://www.dtec.net.au/Flowbench Design Guide.htm

A friend made one before he bought a professional one, he had a square box and a hole in one side of it. he used thin rubber for a seal, and a plexiglas disk to cover the hole. you could then have a solenoid open and close the disk by lifting it. By putting the disk on the out side of the box, any vacuum in the box will help the seal.

 

It's not about the pressure in a 4" pipe, per say, it's about having a large enough bleed to displace the volume of air going through the pipe to in turn raise the pressure back towards atmospheric.

OK you are losing me in this. Atmospheric pressure at sea level on a normal day is about 14.7 psia (Pounds Per Square Inch Atmosphere). So 14.7 PSIA = 407.3016 inches opf Water = 29.929503114 inches of mercury on a normal nice day at sea level.

The vacuum inside an engine's intake manifold, by comparison, can range from zero up to 22 inches Hg or more depending on operating conditions. Vacuum at idle is always high and typically ranges from 16 to 20 inches Hg in most vehicles.The airflow as it mixes with fuel is not a start / stop affair. Especially when you get into multi cylinder four stroke engines. Just the four stroke process of Intake (piston going down with intake valve open and exhaust valve closed), Compression (piston rising up with both intake and exhause valves closed). Ignition or Power (piston going down with both valves closed ) and finally Exhause (piston coming up with exhaust valve open and inlet valve closed). The 4 cycles require two full strokes of the piston to complete. All of this happens in real short order.

I ride motorcycle and years ago went through a few Honda 750 4 cylinder bikes, years before fuel injection I had to tune the manifold pressure on each carburetor to get a nice balanced vacuum on my manifold. This involved placing a manometer on each carburetor. Vacuum is still pressure but only below atmospheric pressure and inlet airflow is really not noticeable as the valves do their thing so I guess I don't understand what you are looking to simulate?

If you could layout what you have in mind in a mechanical / electrical drawing this would likely go better.

Ron

 

The airflow in a four cylinder engine is rather choppy. The diagram below shows what the airflow might look like. There's slight overlap because of valve timing, but largely the waveform looks a lot like that of rectified and unfiltered DC from an AC source. An EIGHT cylinder engine has similar airflow, except that it typically overlaps by 90˚. As you can see from the tops of the waveforms airflow is much smoother.

@Reloadron you mention "inches Hg" (mercury) and "inches H2O" (water). A few years ago I ran a test on a CPAP machine. It's airflow was rated in "CMH2O" (Centimeters of water). The test I ran consisted of the unit under test (UUT) and a clear length of 3/8" tubing filled with dyed water forming a U shape. Where the water balanced (under no pressure or vacuum) I set up a gauge. As I ran the test I measured centimeters of separation between the higher and lower water levels. The UUT was set to 10 cmH2O. On the vacuum side the water rose 5 cm and on the ambient pressure side the water fell 5 cm. Thus, proving the UUT was operating normally.

The diagram below shows how air might flow through an intake tube for both 4 and 8 cylinder engines. I'd imagine a 6 cylinder would be the same, just two less waveforms.