A Bunch Of Hot Air, Or: How To Kind Of Know What You’re Talking About In FRC Pneumatics

My name is Josh, and I’ve been working in automation since 2016. I am currently employed by Festo as an Application Engineer (feel free to shoot me a PM if you ever need Festo help!), primarily helping automotive customers select the right valves, pneumatic actuators, and electric actuators for their machine designs.

The goal of this post is to provide a basic guide to FRC-focused pneumatics systems. Commonly used terms will be defined, some basic best practices will be covered, along with some common pitfalls and FAQs. Other useful resources I’ve stumbled across or been sent by others can be found at the end.

This is not intended to be a definitive guide on how to implement a pneumatics system from nothing, however, one of the resources linked at the end covers this fairly well if that’s what you’re after. I have not evaluated all information in every resource I linked for accuracy, nor am I enough of an expert on all topics to do so.

Definitions have been sourced from my own working knowledge and research, and are targeted at a beginner’s level of understanding. If you have any feedback on terms I may have missed/poorly defined, best practices you have developed, or other useful resources, please chime in!

General Terms
  • Flow rate - a measure of the volume of air that will pass through a component over an amount of time, generally related to port size and component design; typically described by Cv rating or in Standard Cubic Feet per Minute (SCFM)
  • Cv - A coefficient used to describe flow, related to the effective area of the flow path (more info can be found here, but it’s not exactly light reading)
  • SCFM - The volume of air at a specific temperature that flows through a components given a specific drop in pressure across the component (see “standard nominal flow rate” in this document)
Valve Terms


The internals of a 5/2 (five port, two position) single-acting, pilot-operated, body-ported spool valve, from Festo marketing materials with a few minor edits from me (aka the squiggly-looking lines showing flow)

  • Solenoid Valve - a valve that switches the path of air flow using an electromagnetic solenoid
  • Solenoid (From Merriam-Webster) - A coil of wire usually in cylindrical form that when carrying a current acts like a magnet so that a movable core is drawn into the coil when a current flows and that is used especially as a switch or control for a mechanical device (such as a valve)
  • Pilot-operated valve - a type of valve that utilizes air pressure to assist the electromagnetic solenoid in switching the fluid path; This video illustrates the principle well, but please note that it uses a 3 position valve which aren’t commonly used in FRC
  • Position - A working state of a valve; typical FRC valves are two-position, but three-position valves can be used for some interesting functions as well (maybe a post for another time)
  • Port - An opening on the valve to atmosphere; valves will generally have a supply port and varying numbers of working and exhaust ports depending on valve specifics; in the above image, port 1 is the supply port, and the path is out of port two, while air is exhausting from port 4 to port 5
  • Way - paths that the fluid can take into or out of a valve; sometimes used interchangeably with port, depending on how you define exhaust paths
  • Spool - The portion of the valve that is physically moved to change the path of air flow; note that different manufacturers of valves have different approaches to this
  • Single-acting/single solenoid valve - A valve that uses a single solenoid to switch from one position to the next, but then has some sort of spring return to its original state; won’t hold an actuator in position upon disable; see the above image for an example of the internals
  • Double-acting/double solenoid valve - A valve that uses two solenoids to switch between valve positions; will hold the position of whichever solenoid was last activated, persists on disable
  • Body-ported valve - A valve like that in the image above, where working air comes out of the valve body; Convenient for keeping valves as close to actuator as possible, but require additional wiring/plumbing considerations usually
  • Manifold-ported valve - A valve that must be mounted to a manifold, where working ports and supply ports will be out of the bottom of the body and through the manifold; Good for reducing footprint of components with common air supply and single location to run wiring to and from
  • Manifold - A block designed to interface with the ports of a valve; Capable of supplying pressure or power to multiple valves depending on configuration
Actuator Terms
  • Pneumatic Actuator - blanket term for an air-powered device that turns air pressure and flow into motion
  • Cylinder - Most common type of pneumatic actuator used in FRC
  • Piston - frequently, and incorrectly, used to refer to a pneumatic cylinder; actually refers to the sliding part inside the cylinder that is pressurized on either side to extend or retract the cylinder
  • Piston rod - The part of the actuator that extends out of and retracts into the cylinder body; care should be taken to avoid non-axial loads (strong under compressive loads, weak under bending/side loading)
  • Single-acting cylinder - a cylinder that requires pressure to change from its original state (can be normally retracted or normally extended), but then returns by spring force when pressure is no longer applied (similar to a single-acting valve in that it will not persist in its actuated state, but only if pressure is not maintained as opposed to electrical power for the valve)
  • Double-acting cylinder - a cylinder that changes states based on which side of the piston has been pressurized
Threads And Fittings


Image: Tapered and parallel thread interfaces, from this page

  • Tapered and parallel threads - With different pneumatics components you may encounter different types of these two classes of thread; see above image for examples
  • Common tapered threads you may encounter: British Standard Pipe Taper (aka BSPT or R thread), National Pipe Thread (aka NPT), and NPTF (similar to NPT, but more threads-per-inch, frequently found on the end of piston rods); A closer look at the difference between BSPT and NPT can be found here
  • Common parallel threads: British Standard Pipe Parallel (aka BSPP or G thread) and metric threads, such as M3, M5, M7, etc., where the number represents the major diameter of the thread
  • Please note that numbers used in describing threads (G ½, ⅛” NPT, etc) that are non-metric do not necessarily refer to a nominal dimension of the fitting; This page gives a good look at the actual dimensions of different thread types
  • Tapered male threads can be used with female-threaded parallel ports of nominally the same size, i.e. you can use an R 1/2 (BSPT) male fitting in a G 1/2 (BSPP) port, as long as you use an additional sealing element (teflon tape) like you would with any tapered threaded connection
Best Practices

Minimizing Leaks

  • NPT (not NPTF) and R tapered threads require some sort of addition to the threads to create a seal. This is often achieved with teflon tape. Some caution must be taken to ensure a proper wrap, and therefore a proper seal, and to avoid tape fragments clogging up your system. The video on this page from Swagelock demonstrates the process well.
  • Straight/Parallel-thread fittings rely on an o-ring or other sort of element to create a seal between surfaces. This page gives a good overview on different thread types and their sealing methods.
  • Tubing ends should be cut as straight as possible, and should be pushed as far into a push-to-connect fitting as they can be (Order transposed per @GeeTwo’s suggestion). You can get a proper hose cutting tool for <$10 from many places.

Air Consumption Reduction

  • Single-acting cylinders - By utilizing spring force to extend or retract, you’re approximately halving your air volume requirement per sequence; be careful, as this might not be feasible if your application requires significant force in both extension and retraction, or if uncontrolled movement when the robot gets disabled is dangerous or undesirable
  • Use double-acting cylinders without plumbing to the retract port to achieve a similar effect to a single-acting cylinder (depending on the application and desired function, the extend port could also be left open to atmosphere); see this pic from this post and zoom in on the central cylinders for an example

Avoid side-loading your piston rods as much as possible

  • Please, if you’ve read through the rest of this, I make this one simple request: your piston rods will thank you (and they’ll remain much straighter, which only helps keep them extending and retracting quickly and with force!)
  • Using clevices or other cylinder mounts that allow some play in different directions will help with this
  • Look at existing industrial solutions for inspiration
Common Problems and FAQs

Valve Not Switching/Actuator Not Actuating

  • Double check the operating voltage for your valves per the manufacturer, and that the PCM is providing said voltage
  • Make sure any manual overrides a valve has, on the valve body, are not in a locked position preventing the valve from electronically switching
  • Via @Nate_Laverdure: If a brand-new pilot-operated is not behaving as expected, manually actuating the valve may help “unstick” the pilot valve; the valve spool may also have settled into an undesired intermediate position and manually actuating it will help ensure it is put into a correct state

Can I use a single-acting valve with a double-acting cylinder?

  • Yes! Internally, your typical single- and double-acting 5/2 valves are virtually identical aside from how the spool moves; see Spectrum’s Advanced Pneumatics Guide linked below for details on when/why this is desirable

Is [particular valve or actuator] legal?

  • Highly dependent on a given year’s rules; Restrictions in the past have been based around Cv or flow rating, port size, tube size, etc.
  • It should be noted that pneumatics components are generally considered “sacred” by the manual, i.e. they are not allowed to be modified like some other COTs components may be
  • Please read the rules from a given year closely
  • In 2019, some confusion was caused due to this portion of the manual:


Image: A screenshot of rule R84C from section 10.9 of the 2019 FRC Manual Robot Construction Rules

  • The text in parentheses led people to believe that ⅛”, and therefore 3mm, were diameter dimensions to look at in regards to port size. If you were to actually measure the diameter of a ⅛” NPT threaded port, it would measure at approximately .4”, depending on where you measure along the tapered thread. This is because the ⅛” refers to the nominal pipe size of hard pipe that would be used in a fitting, which is based on the pipe’s inner diameter. No, it’s not intuitive. Yes, it is an incredibly mundane topic to try and research. Looking up the dimensions for a given pipe thread size will help you find your answer.
Other resources

FIRST Pneumatics Manaul 2017 - A good overview of the KoP pneumatics components, I haven’t seen a more updated version, so please be conscious of rule changes/legality of components

Spectrum Advanced Pneumatics Guide - For those looking to take steps in strategic component choice, along with some good advice on special applications of pneumatics

AutomationDirect’s Practical Guide To Pneumatics - Primers on Pneumatic Symbols, Actuators, and Valves (among other topics that aren’t as important to FRC). Don’t forget to use your FIRST Voucher!

The Compass Alliance’s Pneumatics Pathway - Beginner Building Blocks and other linked resources cover lots of ground, but keep in mind rules have changed since some of the documents were produced

Mead Handbook - Good overview of several pneumatics topics, including useful charts and sample calculations for determining cylinder speed, required air volume, and other things

[CD Post]: A Beginner’s Guide To Pneumatics - A post from 2014, so be wary of any changes in legal components or rules, but a very thorough walkthrough of how to setup a pneumatics system from scratch

This post, but google doc form.

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Thank you for not telling me that my pneumatic system sucks. (and here’s why)

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Wouldnt you say it blows instead?

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Know what to call a cylinder and what to call a piston.

That’s all you need to know to sound like you know what you’re talking about.

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My go-to person when I have pneumatics questions is typically @Justin_Foss

That guy is a wizard.

Loctite 545 Thread Sealant.

No, it’s not a super-strong threadlocker. It’s mostly a lubricant and sealer.
Yes, you can pressurize a system with it immediately.
You can use it on straight threads and tapered threads.

We’ve used it on 2 or 3 robots now. Zero leaks from threaded fittings. This year we were unbagging robots with 80-100psi in the tanks after weeks of storage.

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One thing I don’t see mentioned enough in regards to pneumatics is that just because you can run them at 60 psi doesn’t mean you have to. If you have your cylinders mounted vertically and have a gravity assist to help with one direction, you can lower the pressure on that side to save air. Also, you can use a larger diameter cylinder with a lower pressure to get the same force with the same amount of air but a lower minimum viable pressure.

For example, we had a pneumatic elevator on our 2015 robot to lift the whole tote stack. We could have used a 1.25" cylinder with 60 psi, but we chose to use a 2" cylinder with 20 psi. Here’s why:

  • With a 2" cylinder pressurized at 20 psi up and 5 psi down, we get 63 lbs of lift force and 15 lbs lowering force. It only takes 6 tanks to keep above 20 psi all match
  • With a 1.25" cylinder pressurized at 60 psi up and 15 down, we get 74 lbs of lift force and 16 lbs of lowering force. But it now takes 15 tanks to keep above the higher 60 psi minimum for the whole match.
  • With a 1.25" cylinder at 60 psi in both directions, we now get an unneccessary 65 lbs of lowering force, and it takes a whopping 26 tanks to keep above 60 psi.
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What calculator did you use?

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This is the beta for the newest version of my AMB Design Spreadsheet. You can find the current version here, which has the same calculator minus a few features. I hope to be releasing the newest version in the next few weeks.

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Do you have a more detailed procedure on how you apply it? I ask because I know some lubricants, if they get in your air lines, can interact with seals in the valve or cylinder and cause them to degrade.

I can’t say I’ve done a deep dive into the materials that are in the most frequently used FRC components (yet?), just a word of caution to anyone going down the lubricant route.

Edit: After looking at the loctite product, it appears that it starts to harden extremely quickly. My concern might have been a little misplaced here.

Thanks for this, good stuff!

A few nitnoids and additions:

  • Cv - main thing to note short of diving into the documentation is that larger Cv allows more air to pass for a given pressure, and therefore can provide more power (energy or work in a given amount of time).
  • In general, a solenoid valve may switch air, water, or any other fluid. For FRC, yes, it switches air.
  • Note that pilot operated valves require sufficient air pressure to operate. Most if not all commonly-used FRC solenoid valves ARE pilot operated and require about 25-40 psi to operate.
  • Body vs Manifold ported valve: note that if your intent in using multiple valves is to increase air flow, you will need to use body-ported (or in some strange cases multiple manifold-ported) valves to get around the single input port of a manifold.
  • Definition of Cylinder: the key thing about a pneumatic cylinder (as opposed to other pneumatic actuators) is that it moves in a straight line, with a rod extending from one side (or in a few cases both sides) of the cylinder body. These rods most commonly have FINE threading on the end. (other actuators rotate, for example)
  • Tubing: I’d suggest putting “ends cut as straight as possible” before “pushed as far into”.
  • Common problems/not actuating: ensure that you have sufficient pressure in your tank to operate your solenoid valve (see piloted valve in definitions)
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No leaks and holding air for weeks sounds amazing. These are the types of tips I love to find on CD.

The How-To videos make application without overapplying look as easy as it sounds.

How easy is it to clean off the threads for subsequent re-use of fittings?
I suppose cleaning both internal and external threads may be required, since it would bond to both?

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@Jeffrafa linked the how-to videos, which are more or less how we apply it. I encourage our students to ensure that the sealant has formed one continuous loop around the fitting threads before installing anything. Note that in the video the leading 1-2 threads are left bare, which we also do.

545, and other sealants in its family, are free of fillers. Fillers are small particles of solid material used for a few different purposes, but what they can do in pneumatic and hydraulic systems is damage o-rings if they get ingested. 545 has no fillers, so this failure mode is not a concern.

Cured 545 is a thermoset plastic, which will not migrate anywhere in the pneumatic system. When tightened into a fitting 545 beings to cure immediately. We have never observed migration of 545 out of a joint, let alone any seal degradation or failures.

545 is formulated to be quite chemically inert. As cured it is compatible with a wide variety of chemicals. If one was so inclined you could do a thorough search of the chemicals listed in the SDS.

In my day job I use 545 on leak testing fixtures and equipment in clean rooms to test inkjet print heads. After years of continuous use of 545 I’ve never seen a single problem.

We use stainless steel wire brushes to clean up fittings, similar to this one. This works really well for PTFE tape too.

It’s good to note the proper procedures for applying 545, which is to clean the mating threads. In FRC however we’re using ~1.2% of the sealant’s 10ksi pressure capacity. So achieving an optimal bond is not required for great FRC performance. This is also why you can use 545 almost immediately after applying it: one only needs to wait a few minutes to reach 1% of cured strength. We have also routinely applied 545 over pre-doped fittings with great results.

For my aforementioned day job we just cleaned the threads with an isopropyl alcohol squirt bottle and let them dry.

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Thanks for expanding @JamesCH95, great info there.

I’ve added a small section on thread types and fittings at the suggestion of @AllenGregoryIV, thanks to everyone who has made comments here and on the google doc!

I am not sure when Discourse locks a post from editing, but I will be sure to keep the google doc up to date and do my best to reflect those changes in the OP.

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Not a problem!

One thing that I forgot to add - improper application of PTFE tape (too close to the fitting end, too much, poorly trimmed ends, etc) can result in chunks of the tape circulating through a robot’s pneumatic system. This can jam solenoid valves, plug regulators, or potentially compromise safety mechanisms. If one chooses to use PTFE tape it must be used very carefully to avoid these risks.

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CD locks edits after 24 hours, so you may want to turn your post into a wiki to avoid the edit lock.

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This is perfect, thanks for the heads-up. Post has been converted to a wiki.

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Something to add which we learned this year: The super-flexible polyurethane tubing from Automation Direct (and others) is really nice to work with, but it is sensitive to heat. If you use it right after the compressor, it might deform enough so that it won’t stay in the fittings anymore! So I recommend using stiffer, higher temperature rated, Nylon or Polypropylene tubing for the run between the compressor and the main regulator.

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To expand on this: we add all the brass fittings we need directly onto the compressor and setup a fan or two blowing across it. This does a good job of keeping the compressor and input air quite cool during long practice sessions and back-to-back finals matches. It’s the difference between seeing even nylon tubes balloon out and the compressors being just warm to the touch.

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Now that the AndyMark 1.1cfm compressor is no longer sold, what’s everyone’s compressor of choice?