Air Flow Control in a system with no pressure/heat

After various searches on air control the closest thing I found was this variable air solenoid control - Project Guidance - Arduino Forum, which involves a pressurized system. This thread recently opened (Flow Control - Project Guidance - Arduino Forum), but due to the slightly different requirement I didn't want to throw my project in.

I want to control the flow of air on a 1.5" valve, in a system with no pressure/heat.

Ball valves exist at this size and are modestly priced: ($9 for 1.5", requires servo.)
http://discountpoolmart.com/index.php?manufacturers_id=44&osCsid=042b251e039e485920742da8b1219eb4

Pros:
Inexpensive
High air flow in ball valve
Air flow can be regulated, vs. on/off

Cons:
No instant on/off (preferred)
Requires servo to control valve
No fail safe/redundancy

My second approach was to use a flow control/irrigation valve, instant open/close, easier to automate. ($45 for 1.5")
http://www.sprinklerwarehouse.com/Hunter-Sprinkler-Irrigation-Valve-p/PGV-151.htm

Pros:
Instant on/off (preferred)
Doesn't require additional parts/labor (such as a servo)
Might be fail safe? (I'd prefer a servo that was open by default, so a failure resulted in an open valve)

Cons:
A bit more expensive
Might restrict airflow
No air regulation

I'm sure there are other approaches..

So that's where I'm at right now, I'm still not sure of the best way to drive this either. I'm a programmer, so EE is somewhat mystical to me, but I'm picking it up as I go along. I'd prefer to spend less than $100 in parts, I currently have an arduino and ethernet shield. Interested to get any and all feedback!

I don't understand what you mean by "no pressure". Air can only move if there is a pressure difference. If you mean a very low pressure, then I wonder if you need a valve at all. What about mounting a flap on a servo arm so that can cover/uncover the orifice.

...R

Hehe, this is true, I had the 150psi reference in the back of my mind when I wrote that. I need to calculate the max pressure I'll anticipate, it's definitely very low.. air conditioning vent low.

I do like the flap idea, but since input/output are PVC plumbing, it wouldn't work without designing a casing. Imagine the current system as a gate (or two) in an exhaust manifold, individually controlled branches (inline).

The irrigation valve is an off the shelf solution, I'd just need to build the driver. 1.5" is optimal, 1" is manageable, but would work best in parallel. I've found 1" valves for around ~$12, not much more than the manual ball valve! Course I'd need two.

The ball valve idea would require work on the servo/motor. Originally I was thinking of mounting a servo to manipulate a ball-valve handle, but I bet I could just mount a motor directly to the ball valve stem. I'd have to find a motor with a good amount of torque, develop a mount, and.. this just sounds like too much work with too many points of failure.

I need to read up on the irrigation valves, I'm sure all my driver related questions are there. I'm reading up on coils and impedance now, but I'm thinking a 9v battery can power the servo.. unless I can get this type of power through the Arduino itself.

You can get geared motors such as these Pololu Metal Gearmotors

But it may make more sense to buy a motorized valve.

...R

isunktheship:
Imagine the current system as a gate (or two) in an exhaust manifold, individually controlled branches (inline).

How hot is this thing going to get, how well does it need to prevent flow in the 'closed' position, and how important is it to you that the whole valve assembly doesn't leak to the outside?

PeterH:
How hot is this thing going to get, how well does it need to prevent flow in the 'closed' position, and how important is it to you that the whole valve assembly doesn't leak to the outside?

Currently it's just room temperature, 40-100F depending on the season, but as such I won't need to worry about condensation. Because this system is simply for redirecting room temperature air in a controlled manner a leak wouldn't be problematic, but I would prefer no leaks.

You won't move a worthwhile amount of air though a 1.5" pipe unless you have a significant pump - which implies noise.

On my boat I move warm air from around the top of my stove through a 6"x 5" duct using a 120mm computer fan slowed down with a resistor. It's almost inaudible and switching off the fan stops the flow. I can run the fan at higher speed but rarely do. It works 24/7 through the winter.

A larger duct would have been better, but I didn't have space for it. Think of how large air conditioning ducts are.

If you have a reasonably sized duct and want to block the flow to favour another branch of the duct a close fitting flap that doesn't actually touch the walls of the duct would probably be quite sufficient.

...R

Robin2:
You won't move a worthwhile amount of air though a 1.5" pipe unless you have a significant pump - which implies noise.

Yeah, the air pump would be in another room, and the solenoids are rated for 150psi

Robin2:
On my boat I move warm air from around the top of my stove through a 6"x 5" duct using a 120mm computer fan slowed down with a resistor. It's almost inaudible and switching off the fan stops the flow. I can run the fan at higher speed but rarely do. It works 24/7 through the winter.

Ah yeah that works, from building computers you can buy them with pots built in too. There's loads of competition for quietest fan, like the Noctuas are silent too.

I have a few items I'm trying to build:
Air Flow controller (open/close in 1"-2" pipe)
Water Flow controller (city water supply, 600GPH, 1"-2" pipe)
Pressurized Air Flow controller (from a SCUBA tank, between first and second stage ~150psi [I believe these exist OTS], or after second stage [similar to Air Flow controller at this point])

Ultimately these would all be able to network, I may change gears to build the water controller as there are loads of resources related to green houses/hydroponics. If many of these valves are OTS I'll need to try my hand with the electronics portion.

I’m afraid you have lost me.

Your most recent post is fundamentally at odds with the title of the thread.

…R

Robin2:
I'm afraid you have lost me.

Your most recent post is fundamentally at odds with the title of the thread.

...R

Baby steps! My first project (air control) will be useful, but will give me a better understanding as how to wire and box a setup. If you'd like to comment on the others it's definitely counter to what my title suggests, but those are on the table.

isunktheship:
give me a better understanding as how to wire and box a setup

So what are you actually asking for help with?

Are you looking for a valve design that lets you controlling low pressure air through a 1" dia pipe? Or a design that lets you control low pressure air through a 6" dia pipe? Or something to control air flowing at 150 psi? Or are you actually looking for help on the electrical and packaging side? At the moment you seem to have some very specific and very unusual requirements and I can't follow what aspect of this you're asking for help with.

I'm in the planning phase, so I'm posting under "Project Guidance". I appreciate all the help I've received, it's sufficient for the Air and Water controllers. When I'm ready to start the next phase I'll post in the Electrical section of the forum.

Title aside I'm also looking for a good manufacturer of solenoid valves for compressed air. I do need to figure out what my thread sizes are and max pressure is, but I would be using the High (or Low) pressure ports from the first stage of a SCUBA regulator. My objective is the same, just control air flow on/off.

Thanks again for all the help!