# Reduce Pnu "slamming"



## beaver state rich (Jan 25, 2014)

On the punch list this year was to upgrade my pirate crypt to Pnu cylinder. The idea is that the front of the crypt drops down to show a canon/pirate during part of our show. Last year we used a reindeer motor to just have the panel drop but then it would have to close manually which left it open during rest of the show. This was lame to have a pirate still around during the HM section. 

My issues is that the PSI required to lift the door back up is around 100. After the cylinder slowly hits the break even point of the lift the result is a violent slam shut. I have the Fright Props speed controller mufflers already and this helps with the lowering of the door but the raising it does not. 

Trigger....R- I- S- E (3") ... SLAM.

Hardware is a 1.25" 8" Fright Props cylinder controlled by their solenoid and speed control mufflers installed 

So.. any ideas? Is there some sort of a buffer anyone is using to slow the "crash" of the cylinder after it hits the break even point of the load?


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## bfjou812 (Aug 15, 2008)

How much does the door weigh? It almost sounds like the cylinder may be too small for the application. You could use a shock absorber located at the top of the door to cushion the rise speed ,but all that will do is cushion the end of the travel. You should be able to control the speed with a speed control mufflers, one on each exhaust port.


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## beaver state rich (Jan 25, 2014)

The door weighs very little, it's 1" foam with 1x2" frame-less than 15 lbs. I'll shoot a short video and post to provide a visual.


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## dstading (Aug 6, 2014)

Is anything binding on the door during it's initial rise that gets freed in the last few inches of travel? Does the cylinder pivot during its operation or is the load always applied in a straight line? All other things being equal (flow, pressure, load, load angle), the cylinder should travel at the same rate throughout its throw. 
Kinda agree with bfjou812 about the cylinder possibly being undersized, but you should see the cylinder struggling all the time.


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## corey872 (Jan 10, 2010)

If it's purely a weight issue, you might try counterbalancing the door with a spring, additional weight offset on a lever arm, etc. A properly balanced movement, should allow you to reduce the pressure needed to activate which should further reduce any abrupt movements.

As an alternative you might try a car window regulator motor. or windshield wiper motor with appropriate linkages. Gear motors like that tend to run a lot smoother as the load changes because even as the motor goes from pushing the prop to being pushed BY it, the gear speed is relatively constant. Whereas the air cylinder can suddenly snap once the load changes. Actually, that is where air cylinders work the best - where you do want a quick snap action - possibly followed by a slow release, or a quick snap back the other way.


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## dstading (Aug 6, 2014)

Counterbalancing is good, that will definitely reduce the pressure needed. I did a bit of homework on this - have you tried reducing pressure and increasing flow? This will allow the cylinder to get to full pressure more quickly in the travel length. If flow is reduced, it will be operating at a lower pressure early in the cycle and then speeding up as pressure increases near the end of the stroke.


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## scarybill (Oct 7, 2012)

Are you regulating the air leaving the cylinder? The flow controls should allow full in, but regulate it coming out. 
Many people put the flow controls on back wards.


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## scarybill (Oct 7, 2012)

This is a male connector flow control, it goes right into the cylinder. It is the only way to go for speed control. They are about 5 bucks from fright props


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## beaver state rich (Jan 25, 2014)

Here is quick video that should illustrate what I am trying to do.

I weighed the door with my fish scale and its 3lbs 10 oz to lift off the ground.

To get the door to lay flat the geometry of the cylinder is pretty much set.

I'm wondering if a set of springs or bungee cords may give it enough initial boost to get it started with less PSI to reduce slamming.


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## scarybill (Oct 7, 2012)

Have you tried to make the arm that the cyl attaches to the door longer?


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## beaver state rich (Jan 25, 2014)

SUCCESS!!!

The bungee cord worked perfectly. The geometry was working against me and a slight assist to get the momentum started was all I needed. I went from 105psi to 45-50 psi.

THANKS!!!!!!!!


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## bfjou812 (Aug 15, 2008)

Just saw the 1st video, the thing that stuck out immediately was the horizontal angle of the cylinder. You needed to get the back of the cylinder up higher than it was .It was too "flat" and couldn't overcome the leverage of the door laying flat. Good to see you found a solution though.


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## ibjeepin (Dec 6, 2008)

bfjou812 said:


> Just saw the 1st video, the thing that stuck out immediately was the horizontal angle of the cylinder. You needed to get the back of the cylinder up higher than it was .It was too "flat" and couldn't overcome the leverage of the door laying flat. Good to see you found a solution though.


I agree the back of the cylinder needs to go at least to the top of the wood its mounted on.

IBJ


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## Monsterman (Sep 12, 2011)

Just a guess, but it looks to me that you need to put the cylinder at more of an angle. You need it to pull in more of and upward motion not a straight back motion. The first attempt where the door does not go up it looks like it is pulling backwards against the hinges more then upwards working with the hinges, if you understand that lol. I had a similar issue with a coffin sitter prop. When in the down position the cylinder was too straight to get the prop to pull up.


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## Monsterman (Sep 12, 2011)

Monsterman said:


> Just a guess, but it looks to me that you need to put the cylinder at more of an angle. You need it to pull in more of and upward motion not a straight back motion. The first attempt where the door does not go up it looks like it is pulling backwards against the hinges more then upwards working with the hinges, if you understand that lol. I had a similar issue with a coffin sitter prop. When in the down position the cylinder was too straight to get the prop to pull up.


argh! sorry about repeating this answer. I did not notice 'page 2'


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## ibjeepin (Dec 6, 2008)

Monsterman said:


> argh! sorry about repeating this answer. I did not notice 'page 2'


Me, I would just call it an alzheimer's moment! LOL Happens to me all the time!


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## craigsrobotics (Oct 12, 2009)

Put the flow controls on the exhaust ports of the valve....you need to control the exhaust at the valve not the cylinder.


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## Jackyl48 (Nov 13, 2013)

One thing that might help is mounting the cylinder in the center of the door instead of having it on the side. That way it lifts the door evenly instead of twisting it. Which might result in lower pressure required.


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