Placing a Tank after a solenoid valve

[apples000]

So our team's planning on using pneumatics to launch the ball, but as others have noted, there's not enough flow rate. So, what we do is lock down the cylinder, open the solenoid valve which fills a small tank, then unlock the cylinder. However, the team is convinced it's illegal, but I can't really find any rules saying you can't. Has anybody else done this before?

[Team 4057]

so long as you don't use multiple solenoids you look ok to me. the rule your team mates are talking about refers back to previous years that prohibits long runs of tubing to gain extra air storage.

[Wire Monkey]

It looks like R78 says you can't.

If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be used in accordance with this section, as illustrated in Figure 4-15.

The drawing has the tank before the solenoid. IF the rule says it must be done EXACTLY like this picture then I don't think it is legal.

[Madison]

The following is a schematic of the pneumatic system we used in 2012 for our catapult. It was, of course, completely legal and did have storage tanks on the low-pressure side of the system.

http://www.chiefdelphi.com/forums/attachment.php?attachmentid=12089&d=1330055105

We did use a valve between the storage tanks and the cylinder, so the implementation you're suggesting is a little bit different. I can't speak to the legality of impeding the motion of a cylinder mechanically, though there doesn't appear to be any rule prohibiting that at a quick glance.

[FrankJ]

It looks like R78 says you can't.

If pneumatic COMPONENTS are used, the following items are required as part of the pneumatic circuit and must be used in accordance with this section, as illustrated in Figure 4-15.

The drawing has the tank before the solenoid. IF the rule says it must be done EXACTLY like this picture then I don't think it is legal.

So the picture does not show cylinders or solenoid valves?

Figure 4-17 shows a low pressure accumulator.

A little heavier, but unquestionably legal: Use a cylinder with a longer stroke than is required & don't retract it fully.

[BBray_T1296]

Lets take this by the rules (http://frc-manual.usfirst.org/viewItem/3#4):

R74: Pass, parts are legal
R75: Pass, tanks are rated for 125+PSI
R76: Pass, parts are unaltered
R77: Pass, parts are legal
R78: Pass, this rule lists the parts of a pneumatic circuit, but not in any specific order
R79: N/A not a compressor
R80: N/A not a compressor
R81: Pass, not operating above 120PSI
R82: Pass, beyond the primary regulator, and working at or below 60PSI
R83: Pass, though white-listed to be useable in 120PSI, not specifically required to be there
R84: N/A not a pressure gauge
R85: N/A always on-board
R86: Pass operating at 60PSI or less
R87: N/A not a relief valve
R88: N/A not a pressure switch
R89: N/A not a vent plug
R90: Pass, operating on a single solenoid
No blue boxes are applicable either.

So, since this passes all applicable rules related to pneumatic, I say it IS legal

[DonRotolo]

Consider alternative ways of 'assisting' your cylinder's extension with, say, latex tubing.

EDIT: If you place a storage tank after a solenoid valve, will THE one Pressure Vent Plug reliably vent all stored pneumatic pressure from the system when the release valve is opened? If not, R89 will be violated.

[MechEng83]

Consider alternative ways of 'assisting' your cylinder's extension with, say, latex tubing.

EDIT: If you place a storage tank after a solenoid valve, will THE one Pressure Vent Plug reliably vent all stored pneumatic pressure from the system when the release valve is opened? If not, R89 will be violated.

The pneumatic valves from FIRST Choice last year (and possibly this year, as I don't have access due to school STILL being closed...:mad: ) violate this rule. The valves have a neutral position, which means that unless the solenoid is active, the pressure from both sides is dead-headed. This is different behavior from the KoP valves from several years ago.

[KevinG]

Consider alternative ways of 'assisting' your cylinder's extension with, say, latex tubing.

EDIT: If you place a storage tank after a solenoid valve, will THE one Pressure Vent Plug reliably vent all stored pneumatic pressure from the system when the release valve is opened? If not, R89 will be violated.

Why would the amount of air located on one side of the solenoid valve matter? There's 60 psi of air contained within the tubing, and that has to vent just as reliably as air contained in accumulators.

[ToddF]

It's our opinion that as the rules are written, an accumulator downstream of the solenoid valve is legal. If a QA answer rules this out, it is legal to connect multiple cylinders to a single valve. Just pick one with the internal volume of the tank you want, and plug one of the ports. Viola, instant accumulator. Not as weight efficient as a tank, but performs the same function.

Or, as someone else mentioned, pick a cylinder with a large internal volume and only plan to use half (or less) of the stroke. (This is actually the most weight efficient solution of all.)

[Al Skierkiewicz]

R89
The pressure vent plug must be:
A. connected to the pneumatic circuit such that, when manually operated, it will vent to the atmosphere to relieve all stored pressure, and
B. placed on the ROBOT so that it is visible and easily accessible.
If the compressor is not used on the ROBOT, then an additional pressure vent plug must be connected to the
high-pressure portion of the pneumatic circuit off-board the ROBOT with the compressor (see R79).

Air pressure in a storage tank is "stored" in the rule above.

[FrankJ]

So using the accumulator as described is OK as long as the vent valve will release its pressure?

[Al Skierkiewicz]

I have to ask the OP to be sure...
OP, You are using a valve to charge a tank and operate a cylinder in the same circuit? Is that what I am reading?

Madison,
In looking at your drawing, I do not see how the stored pressure can be vented immediately by opening the manually operated valve. Should there be a failure in either of the regulators, opening the valve leaves high pressure air still in the tanks. While that may have passed inspection at your events in 2012, I do not think it was legal in 2012 or now.

Please ask the question of the Q&A.

[Madison]

I have to ask the OP to be sure...
OP, You are using a valve to charge a tank and operate a cylinder in the same circuit? Is that what I am reading?

Madison,
In looking at your drawing, I do not see how the stored pressure can be vented immediately by opening the manually operated valve. Should there be a failure in either of the regulators, opening the valve leaves high pressure air still in the tanks. While that may have passed inspection at your events in 2012, I do not think it was legal in 2012 or now.

Please ask the question of the Q&A.

Al -- Unfortunately, pneumatics isn't my area of expertise, so I can't provide a definitive answer for your concern. I do know, however, that we were able to vent all the pressure from the system with the single release valve. I'll ask the folks who were responsible for this to provide some clarification. It may be that the system was changed after this schematic was created.

-Madison

[gpetilli]

I have to ask the OP to be sure...
OP, You are using a valve to charge a tank and operate a cylinder in the same circuit? Is that what I am reading?

Madison,
In looking at your drawing, I do not see how the stored pressure can be vented immediately by opening the manually operated valve. Should there be a failure in either of the regulators, opening the valve leaves high pressure air still in the tanks. While that may have passed inspection at your events in 2012, I do not think it was legal in 2012 or now.

Please ask the question of the Q&A.

I too am not an expert, but I believe the standard FRC solenoids use a supply "pilot" which means that if the input air pressure goes away (think manual dump) then the solenoid opens allowing the output air to back through the output to the input. This works only if there are no check values in the system and does not depend on any electrical signals. We have had issues in the past that if the working pressure is too low, there is not enough energy to "engage the pilot" and the solenoid does not activate. If I am correct, then this would allow the low pressure storage tank to vent when the manual release is opened.

[Richard.Varone]

We actually did this in 2008 and it was legal, but it's possible the rules have changed so this sounds like a good Q&A to me.

[Peter Matteson]

Mechanically locking a cylinder and keeping the valve open won't do anything.

Once you have 60 psi air in the area of the cylinder it can fill it will stop flowing. Adding low pressure volume does nothing but make your compressor work harder for no reason. The reason you have high pressure storage is the change in volume of the air as it expands to a lower pressure acts as energy storage. Without the expansion just oure volume does nothing.

Please rethink your plan and consult a mentor that has some experience in fluid dynamics.

[Mr V]

I too am not an expert, but I believe the standard FRC solenoids use a supply "pilot" which means that if the input air pressure goes away (think manual dump) then the solenoid opens allowing the output air to back through the output to the input. This works only if there are no check values in the system and does not depend on any electrical signals. We have had issues in the past that if the working pressure is too low, there is not enough energy to "engage the pilot" and the solenoid does not activate. If I am correct, then this would allow the low pressure storage tank to vent when the manual release is opened.

Yes the common solenoids are air piloted but that is not relevant to their operation. They just use air pressure to move the shuttle, once the shuttle is moved it stays there and w/o enough air pressure they can't move the shuttle.

Since the shuttle stays in the same position the pressure on the working side of the valve can vent back through the valve. So yes tanks on the working side of a commonly used FRC solenoid will vent assuming as you noted that there aren't any check valves added into the system.

[pmangels17]

Mechanically locking a cylinder and keeping the valve open won't do anything.

Once you have 60 psi air in the area of the cylinder it can fill it will stop flowing. Adding low pressure volume does nothing but make your compressor work harder for no reason. The reason you have high pressure storage is the change in volume of the air as it expands to a lower pressure acts as energy storage. Without the expansion just oure volume does nothing.

Please rethink your plan and consult a mentor that has some experience in fluid dynamics.

In 2008 we used a lock and air tanks on the cylinder because the flow rate through the solenoid wasn't fast enough to accelerate the ball quickly. The extra tanks were mounted using brass fitting to allow a larger volume of air to be stored, so that when the piston is released, the air can flow faster into the cylinder, thus moving the piston faster. This gave us more power and a quicker shot. Adding a tank between the valve and cylinder facilitates a more powerful shot.

[FrankJ]

Think of this way. You use cylinder that has more stroke than you need. The start position is mid way in the cylinder. You effectively use part of the cylinder as the accumulator. And you don't have that pesky 1/4 tube slowing things down. If the vent valve can dump all the pressure, you should be legal. If it doesn't then the design is not legal regardless of the legality of the individual parts.

This is safer than using a big spring for your stored energy since you can relieve the pressure, getting rid of the stored energy. The catapult is ultimately going to have the stored energy to throw the ball at the required speed regardless of the method used. So the wise thing to do is thing about how to safely handle that energy.

[Richard.Varone]

For those interested this was actually a prototype from 2008 which was the first thing we tested after kickoff. This is an 8" with a 1 1/2" bore and it shoots the ball about 7ft ish into the air.

If anyone would like more info on it let me know and maybe we can post a vid or something along those lines.


EDIT: DISCLAIMER - This was legal in 2008, we haven't looked into it's legality in 2014.

[Peter Matteson]

In 2008 we used a lock and air tanks on the cylinder because the flow rate through the solenoid wasn't fast enough to accelerate the ball quickly. The extra tanks were mounted using brass fitting to allow a larger volume of air to be stored, so that when the piston is released, the air can flow faster into the cylinder, thus moving the piston faster. This gave us more power and a quicker shot. Adding a tank between the valve and cylinder facilitates a more powerful shot.

The flow restriction is still the valve. Your are not getting full working pressure but something signifigantly less that weakens quickly as the air expands. Again going back to my point you are get the force you think you are when you do this, unless you have calculated out the pressure when the volume you trap fully expands.

[Al Skierkiewicz]

I am looking at this more from a safe design that plans for failures view. If the system dump valve is downstream from a regulator(s) that potentially could plug in a failure, then the valve couldn't release all system pressure. I believe that is what the original rule was addressing. With working regulators, system pressure would be released.

[FrankJ]

Q/A Q62 addresses this.
Q62 Q. Is it legal to have air storage tanks (accumulators): A) On the "working" pressure side of the regulator? and/or B) Between a solenoid valve and the pneumatic cylinder(s)? I can find nothing in the rules prohibiting either of these cases.

A. There are no Rules explicitly prohibiting either scenario.

[ToddF]

The flow restriction is still the valve. Your are not getting full working pressure but something signifigantly less that weakens quickly as the air expands. Again going back to my point you are get the force you think you are when you do this, unless you have calculated out the pressure when the volume you trap fully expands.

Valve flow only matters if the reservoir volume is small compared to the cylinder displacement volume. If I have a 5 gallon low pressure reservoir, and a tiny cylinder with only 1cc of stroke volume, flow through the valve doesn't matter at all during cylinder extension (assuming a mechanical trigger restraining a pre-charged cylinder from actuating). At the other extreme, a 6 inch diameter cylinder with a 12 inch stroke having a reservoir composed only of the hose feeding it, the valve flow matters a great deal.

The trick is selecting an appropriate reservoir volume that balances the need for a fast stroke with the time needed to recharge the reservoir after venting for retraction.

[Ed Sparks]

For those interested this was actually a prototype from 2008 which was the first thing we tested after kickoff. This is an 8" with a 1 1/2" bore and it shoots the ball about 7ft ish into the air.

If anyone would like more info on it let me know and maybe we can post a vid or something along those lines.


EDIT: DISCLAIMER - This was legal in 2008, we haven't looked into it's legality in 2014.

I see a potential problem with this device depending on how the system is pneumatically controlled. The cylinder may be considered a second compressor if it restores the air used to push the plunger back into the storage devices when the plunger is re-cocked. In this case, I'm assuming something mechanical is re-cocking the cylinder. A solenoid valve would have exhausted the air to atmosphere in both the forward stroke and reverse stroke.

[Richard.Varone]

I see a potential problem with this device depending on how the system is pneumatically controlled. The cylinder may be considered a second compressor if it restores the air used to push the plunger back into the storage devices when the plunger is re-cocked. In this case, I'm assuming something mechanical is re-cocking the cylinder. A solenoid valve would have exhausted the air to atmosphere in both the forward stroke and reverse stroke.

The cylinder retracted with gravity/a small spring, the valve was open in this condition so the pushed air never re-entered the system

EDIT: Also we've found that in a system like this it's vital to not have any fittings on the other end of cylinder

[Al Skierkiewicz]

In rereading this thread and thinking always about safe operation, the precharged and locked cylinder makes me wonder what happens when the vent plug valve is opened. (I do a lot of "what if" analysis. Sorry, but that is what I do) So these are my questions as I consider operation...
1. Is there ever a chance that the locking cylinder could release the piston as system pressure is vented?
2. Is there a mechanical lock that prevents uncontrolled movement when the robot is powered down?
3. Is the robot carried off the field with the cylinder under pressure and what happens if the robot is accidentally dropped or shocked?
4. When the cylinder moves, is the movement exposed to the outside of the robot?
5. Knowing that the PVC storage tanks have failed in the past (from external forces), are they being used as intended with rigid fittings to a moving cylinder?

Did I miss anything?

[Richard.Varone]

Not sure if this was directed towards me or just in general but:

1. Is there ever a chance that the locking cylinder could release the piston as system pressure is vented?

This was a while ago so my memory might be a bit shaky, but I believe that the trigger was designed such that when the cylinder was pressurized it could only release by powering the lock in the other direction.

2. Is there a mechanical lock that prevents uncontrolled movement when the robot is powered down?

We had a pin that we would install and remove on the field before and after the match

3. Is the robot carried off the field with the cylinder under pressure and what happens if the robot is accidentally dropped or shocked?

Regardless of the year/robot we always open the main release valve before taking the robot off the field.

4. When the cylinder moves, is the movement exposed to the outside of the robot?

Ours was positioned towards the back of the robot and was always within the frame.

5. Knowing that the PVC storage tanks have failed in the past (from external forces), are they being used as intended with rigid fittings to a moving cylinder?

We use and I'd also recommend that anyone doing this setup use metal storage tanks and brass fittings, along with making sure that it is securely mounted so that the robot is taking the recoil and not the pneumatic system.

This setup had potential to be pretty dangerous and extreme caution should be taken into it's design and execution. While it was able to be dry fired we never recommended it, hitting the ball acted as a dampener taking a lot of the stress of the shot. Another point in the safety of a device like this is to attach a rope from the robot to the end of what ever is on the piston.

Now in terms of safety, this years ball is half the size, and with our testing we were able to use a cylinder half the size which makes for a safer implementation :D

[ToddF]

I see a potential problem with this device depending on how the system is pneumatically controlled. The cylinder may be considered a second compressor if it restores the air used to push the plunger back into the storage devices when the plunger is re-cocked. In this case, I'm assuming something mechanical is re-cocking the cylinder. A solenoid valve would have exhausted the air to atmosphere in both the forward stroke and reverse stroke.

Teams implementing a system such as this need to ensure that when the cylinder is "recocked", the pressure side of the piston is vented to atmosphere. It is possible to use a winch type system to recock the mechanical latch. If the solenoid valve were in the closed position, the recocking action could raise the pressure between the cylinder and the valve over the allowable low pressure limit (or, depending on the geometry, over the high pressure limit). This could possibly cause a failure in whatever is the "weakest link" in the low pressure system.

If we go this route, we won't use a recocking mechanism that is capable of overpressurizing the low pressure side of the system. If your team does so, I would highly suggest installing a pressure relief valve set at 60psi between your solenoid and the catapult cylinder. This will help keep you legal and safe.

[Al Skierkiewicz]

Rich,
It was a general, thinking out loud, post. It is nice to know you were thinking along the same lines when the system was designed.

[MartyG33]

What types of tubing can we use? Can we use copper piping for our entire system if we want?

Also how do I post a new thread?

[EricH]

What types of tubing can we use? Can we use copper piping for our entire system if we want?

Also how do I post a new thread?

Last question first: Click the big purple square in the top left of each page. Scroll down to the subforum you think is most appropriate, click it, and click the "new post" at the top of the page.


Now. The rules question.

First answer: Did you read the Manual? Your first question is answered quite clearly by R77E--and your second question will be answered by reading the rest of R77.

[MartyG33]

[QUOTE=EricH;1332248]Last question first: Click the big purple square in the top left of each page. Scroll down to the subforum you think is most appropriate, click it, and click the "new post" at the top of the page.


Now. The rules question.

First answer: Did you read the Manual? Your first question is answered quite clearly by R77E--and your second question will be answered by reading the rest of R77.[/QUOT

Yes, but it only says functionally the same. Stiff copper would function the same as the tubing without the flexibility.

[cgmv123]

Yes, but it only says functionally the same. Stiff copper would function the same as the tubing without the flexibility.

If you think the manual is ambiguous, that's when you ask on Q&A. Chief Delphi is not Q&A.

That said, I question your desire to use copper tubing. Copper is heavy. I'm happy to use the plastic tubing provided in the KOP, since it weighs next to nothing.

[Al Skierkiewicz]

Marty,
What Eric pointed you to is this...
E. Additional pneumatic tubing, with a maximum 0.160 in. inside diameter, functionally equivalent to that provided in the KOP