Fixing a SLOW Leak?

Hello CD community!

So we fired up our robot’s pneumatic system today. Everything worked however our pressure drops from 120psi to 0psi over the course of about 3 minutes. This means one very slow leak or a few very slow leaks…’

We originally thought “Oh well 3 min is a long time it wont hurt our performance over the course of a 2 min match.” However we are realizing that if we want to fill our air tank pre match and have it start the match at 120psi, we would prefer to eliminate the leak(s).

Does anyone have any tips on finding a leak so small that one cannot feel the loss of air with their fingertips or hear it?

Thanks in advance!

Dr stethoscope and a spray bottle of soapy water. Spray your connections and look/listen for air bubbles/leaks.

Also make sure all your hoses are cut straight and pushed into your connections tight. An angled cut at the end of the tube is just asking for a leak. If need be you can buy pneumatic tubing cutters that give a nice clean edge everytime.

Also make sure to screw down all connectors, especially into manifolds.

3 min to loose all pressure? That seems pretty fast to me. I’m surprised you can’t hear it.

What solenoid are you using and how did you tighten the connectors on them?

I’d suggest isolating sections of the pressurized system and testing each section for leaks before moving on to the next section.


  • compressor/regulator/dump valve/pressure switch/gauge
    Plug all regulator outputs-use Teflon tape everywhere
    Fix all leaks
  • add a storage tank
    Fix all leaks
  • add a solenoid/cylinder (plug other tubing)
    Fix all leaks
  • etc

Plan for slow match starts to take up even more time.

A good pneumatics system will hold pressure overnight.

I can’t resist.

Does anyone associated with the team have a swimming pool?


It ain’t supposed to leak at all if done right. Last year our robot came back from champs with 60 PSI in the tanks. In July.

The best tip is using the soap bubbles, even if you dont hear the leak.

Thanks for all of the suggestions! I didn’t know it was possible to get the leaking eliminated entirely! We will take some time to carefully go through the system and tidy it up.

We did this today…started at around 10 am, got it leak free by 2pm. Long day! We isolated the system, and discovered that one of the old solenoid valves was leaking. Replaced it, still leaking slowly, found that the safety pressure relief valve was leaking. Replaced it…then we still had a leak, could not find it, replaced the entire regulator/gauge/switch assembly with another one. Found a leak in the replacement, the manual release valve was leaking, it had a bad O ring inside. Once we replaced that, it works fine.

Soapy bubbles help!

You have bunch of solutions, take time, isolate and conquer. If you are using old connectors, check them, wear and tear makes time tiny bit over sized. Before you spray soap water, please make sure your electrical components are covered.

I’m assuming you’re teflon taping your various threaded connections. Mistakes I’ve seen on robots and professionally:

  • Tubing cut crooked with wire cutters.
  • 5+ wraps of teflon, 2-3 is enough.
  • Bad, damaged, or poorly seated o-rings + gaskets.
  • Missing blank plate on manifold replaced with blue tape. No, I don’t know why.
  • Loose anything/everything.
  • OVER tightened fittings, causing cracks or deformations. Decently snug is about right. If you’re straining/risking a hernia, it’s definitely too tight.

Our usual standard was less than 5psi drop overnight and pneumatics wasn’t done till they could hit that.

That’s the part we always have to check. I was visualizing the connection, and thinking manifold. The ports to the solenoids we have are threaded, and need to be tightened down.

Two More Hints:

  1. Pneumatic Parts DO wear out - how old are the vales, etc you are using?

  2. Soapy Bubbles- the easy way - Ever seen those fancy hand soap dispensers that dispense a foam instead of liquid or gel? They work GREAT for detecting pneumatic leaks. Just apply the foam to your joints. It sticks (doesn’t drip), is easy to clean up and immediately shows you where the leak is. I keep a bottle in my tool box just for that purpose (and I can use it to wash hands too).

We found a leaking pneumatic cylinder in our system. We have no idea how old it was, but I suspect the seals dry out eventually, especially in our dry Wisconsin winter air. The leak appeared to get worse as the season went on. And it did indeed cause our autonomous routine to fail when we started out with less pressure than required after waiting through one of those pre-match delays. There is a special oil for pneumatic tools you might try if you suspect this is the problem.

HI Sam.
One of the simplest tools to help locate the leak in actually part of the pneumatics system. Just use a 2-3 ft. piece of the tubing like a stethoscope. Put one end in your ear and use the other to listen at each location you suspect might have a leak.
Soapy water is good too, but can be messy.

Freshly cut, squared off tube ends are very important at each Junction. Properly taped and tightened fittings is crucial as well.

This is good thinking.

Consider the following situation: at an official event there is often a break or ceremony, at which a VIP speaker is extremely loquacious. Assume your robot is one of six on the field during this important delay. The pneumatic system must hold its air until the VIP has used up all of his.

Quite a few here on CD have been in this situation.

3 minutes sounds pretty fast to me too, I think you’ve got most everything covered but one thing to check too is that everything is connected with correctly sized fittings. Like nuts and bolts those fittings come in metric and american sizes and the two can look very similar to the naked eye but one might not hold the tube as tightly as it should.