T-Shirt cannon AC problem

[KGood]

Our team is trying to make a mounted t-shirt launcher, but we're running into problems with the sprinkler head we're using. We want to mount it to the robot and use the power distribution board but that uses DC, and the sprinkler head requires AC.

So, my question is: If we use 24v of DC from the power distribution board, is there any possible harm that come as a result? The sprinkler head has no circuitry...it's basically just a magnetic release valve, but I wanted to be sure.

Thanks!

[billbo911]

Our experience with the 24vac sprinkler valves is that they operate just fine on 12vdc. That is, if you only power them long enough to launch the shirt. We used a Spike relay to power the valve. It can easily handle the current and has no problem cycling the valve quickly.

We found that you can actually save a lot of battery drain by just cycling the valve open for .1 seconds. How does that save on the battery? In our case, it prevented us from having to completely recharge the pressure tank. Leaving it open for one full second would drain the tank.

[Josh Drake]

Our was made using the spikes and 12VDC too.

[JohnFogarty]

Ok...what we did is we don't use sprinkler electric valve at all. we feet the air into a dump tank on the back of our gun and have a release valve which is a regular legal solenoid. And our dump tank is double layered schedule 80 pressure rated PVC tested at 600psi but never goes above 100psi due to the fact the FIRST regulators won't let us.


This works for us we shot a full football field length at 60psi

[JamesCH95]

Do some math and programming and make a Victor/Jag output AC power

[Alan Anderson]

Originally Posted by John_1102

Ok...what we did is we don't use sprinkler electric valve at all. we feet the air into a dump tank on the back of our gun and have a release valve which is a regular legal solenoid.

I don't see anything I recognize as a FIRST-legal solenoid valve in the photos you gave. Can you be more specific about what you're using?

[Peter Matteson]

Originally Posted by KGood

Our team is trying to make a mounted t-shirt launcher, but we're running into problems with the sprinkler head we're using. We want to mount it to the robot and use the power distribution board but that uses DC, and the sprinkler head requires AC.

So, my question is: If we use 24v of DC from the power distribution board, is there any possible harm that come as a result? The sprinkler head has no circuitry...it's basically just a magnetic release valve, but I wanted to be sure.

Thanks!

Yes there are potential problems. On a project at work we were accidentally supplied 24 VDC valves in place of the 24 VAC valves we ordered, BTW 24 VAC is standard for HVAC applications. They were not caught at recieving inspection. We powered the valves on and all they did was chatter until the seats failed.

You should either use a transformer/inverter to correct the voltage to AC or get a new solenoid. You might be able to purchase and identical DC coil from the manufacturer.

[dtengineering]

Hoo boy. PVC cannons.....

There have been a number of threads (and discussion on other sites) related to the use of PVC in pneumatic cannons.

Many knowledgable people consider the use of PVC with compressed air to be dangerous due to the fact that it fails in a brittle fashion, potentially creating shrapnel. They point out that the ratings on PVC are for liquids, which, being non-compressible, do not have the same potential to explode, and are rated for static pressures. The firing of a t-shirt concievably creates unanticipated impact forces and sudden pressure changes. They also point to the potential for failures at joints and caps, and have provided some convincing anecdotal reports of failures.

Others have reported the successful use of PVC in pneumatic cannons over an extended period of time and confidence that using a sufficiently high safety factor should keep the PVC from failing.

And, of course, advocates for both sides of the argument are very confident that they are correct! (Personally, I've had good success using PVC, but in an abundance of caution have replaced the high-pressure compressed air storage side of our system with black iron pipe, which IS rated for compressed air use.)

Rather than having this thread turn into another "PVC is Dangerous!"/"Not if your're careful." thread, I'll suggest we just encourage people to do their own research and make their own informed decisions.

On the main topic... we've had good luck using 12VDC from a spike to fire our sprinkler valve.

Jason

[Howman]

Using a DC solenoid in place of an AC one is problematic because it lacks the shading coil and/or light spring needed to maintain the armature's position as the AC current crosses zero every half cycle. The DC solenoid being driven with an AC voltage may not open completely, or if it does it will begin to close as soon as the current gets close to zero, hence the chattering.
On the other hand, supplying 24VDC voltage to a 24VAC solenoid is perfectly ok.

[J@GMFlint]

Others are correct about applying DC to similar AC coils for light duty such as this application. My limited experience with my own irrigation system combined with the lower AC power ratings and my elect. background lead me to believe that we could safely try 12VDC before exploring 24 VAC power inversion options, and sure enough it works for our valves!

We use an off the shelf 1" rainbird valve, that looks very similar to what you have. I would suggest you simply remove the coil from your valve so that you can see the poppet and apply std. 12VDC. If the poppet retracts and holds you are good to go! A spike should work well to trigger the solenoid/valve. Put an ammeter on if you are concerned about the draw. For added comfort, since these were not rated for this particular duty, we do not leave the sols. energized for very long after each shot.

[Jester Jackster]

good luck with the cannon