The Ten Step Troubleshooting Process (Excavator)
Objectives
- Demonstrate that a logical and deliberate approach to troubleshooting is highly efficient and effective.
- Explain the Ten Step Troubleshooting Process (TSTP).
- Walk through a practical example using the TSTP.
The Ten Step Troubleshooting Process
The TSTP is a logical series of steps that can be adapted to nearly any troubleshooting problem, and followed for an efficient and effective equipment fix. In this module we will look at the TSTP as a hydraulic system troubleshooting aid, but you could easily adapt it to other challenges, including electrical issues, pneumatic systems, and process problems.
It's Go Time!
The worst thing about unexpected equipment failure is the amount of drama and chaos that usually comes with it. Everyone wants an immediate fix, and everything is depending on you, the troubleshooter, to make that happen.
You might feel pressure to be this guy - at least he's doing something, right?
This troubleshooting style is often called Guess and Check or Hit or Miss.
It has a couple of advantages, and some obvious disadvantages.
Pros
- You might get lucky and make the correct repair quickly.
- Everyone can see that you're working hard on the problem.
Cons
- You might NOT get lucky - the correct repair might be hours, days or even weeks away.
- You are likely to replace a lot of parts unnecessarily.
- You might fix the problem causing the breakdown, but you may not have addressed the root cause of that problem - the breakdown might happen again tomorrow or next week.
- All of the other parts replacements and incorrect repairs can create new repair-induced failures.
- You might injure yourself, as often happens when rushing or when working without a plan.
Case Study: Slow Bucket Curl
The Ten Step Troubleshooting Process is an alternative to Guess and Check Troubleshooting. Let's see how it works.
Step 1
Define the Nature of the Problem
The first step when following the hydraulic TSTP is to decide whether this is a Flow, Pressure, or Directional Problem.
Flow Problem
Actuators move too fast, or too slowly.
Pressure Problem
When tackling the heaviest loads, actuators:- stall (in a kinetic state)
- can't maintain position (in a static state)
Directional Problem
System normal in one direction only. Reverse function is compromised or non-existent.
Seems like our slow bucket curl fits the description of a flow problem.
Step 2
Consult the Schematic, Manuals & Maintenance Records
Take the Lead
Get a head start on this step before there's a problem!
- Verify that you have the correct schematic and repair manual for that machine.
- Arrange to replace documents that are missing or hopelessly out of date.
- Be a leader in your department by taking charge and getting this done!
An accurate schematic is an incredibly powerful troubleshooting tool. It can provide:
- A list of all of the components in the system, often including exact part numbers, codes and system-specific settings.
- A diagram of the relationships/connections between system components.
- The exact location of test-points.
- A planning tool for isolating sub-circuits for testing purposes.
We have an accurate schematic for our excavator, which will be helpful. Take a moment to look it over and get familiar with the machine's hydraulic systems.
Review The Schematic
Touch each glowing circle to quickly review some system details.
Common P Line
All of the excavator cylinders are supplied from the same "P" line inside the valve manifold.
Common T Line
The directional control valves (DCVs) all exhaust to the same "T" line that is routed back to tank.
Proportional Flow
Each directional valve provides variable speed (proportional flow) control for cylinder extend and retract motions.
Variable Current Solenoids
The proportional directional valves are operated by variable current solenoids.
Travel Stops
The directional valves feature adjustable screw stops to limit the maximum travel of the valve spool in each direction.
Shock Relief
Each cylinder sub-circuit has a pair of shock relief valves.
Anti-Cavitation Valves
Each cylinder sub-circuit has a pair of anti-cavitation valves.
Gather Resources
It's also helpful to grab the manufacturer's manual, and the maintenance records, if they are available. The manual will help you out with component specifics and adjustment settings. The maintenance records will supply the history of this system. Did this bucket curl problem always exist, and has slowly been getting worse, or did it suddenly present itself out of nowhere?
Unfortunately, in our case the maintenance records don't include cylinder cycle timings, so it's more difficult to know what the normal bucket curl time is for comparison. It seems safest to assume that this problem is new. It's extreme, and there is no sign of an operator complaint before now.
Step 3
List Suspect Components
In step one, you determined that the slow bucket curl is likely a flow problem, so you should concentrate on failures that could cause a flow problem, rather than a pressure or directional problem. Now it's time to make a list of all of the components where a failure could cause any flow problem, not just the slow bucket curl.
As you consider each component, ask yourself these questions:
- What is this component?
- What does it do?
- What can go wrong with it?
- Can that cause a flow problem?
Bonus!
This is a list that you will only have to create once.
In fact, you can create this list, along with a list for pressure problems, and one for directional problems, before there is a malfunction. Once you have it, this list becomes another tool in your troubleshooting kit.
Make a Flow Problem Suspect List
Touch the glowing circles to examine each component and consider whether it belongs on your Flow Problem Suspect List.
Reservoir
(25)
What Does It Do? The tank holds surplus oil at atmospheric pressure.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Could be overfilled | No |
| Could be underfilled | Yes |
| Breather could be plugged | Yes |
| Strainer could be plugged | Yes |
Pump
(1)
What Does It Do? The pump supplies flow to the system.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Produce too much flow | Yes |
| Produce too little flow | Yes |
| Produce no flow | Yes |
Relief Valve
(2)
What Does It Do? The relief valve limits maximum system pressure.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Sticks fully open | Yes |
| Sticks fully closed | No |
| Sticks partially open | Yes |
Load Holding Check Valve
(3, 5, 7)
What Does It Do? Prevents drop of heavily loaded cylinder being raised if a more lightly loaded cylinder is activated at the same time.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Sticks fully open | No |
| Sticks Closed | Yes |
| Sticks Partially Open | Yes |
Directional Control Valve
(4, 6, 8)
What Does It Do? Directs flow to a cylinder.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Leak to Tank in Neutral | Yes |
| Incomplete Travel - Caused by Contamination, Solenoids or Spool Travel Stops | Yes |
| Incorrect Direction of Travel | No |
Relief Valve (Shock Valve)
(9, 10, 13, 14, 17, 18)
What Does It Do? This valve limits maximum pressure in the cylinder when the DCVs are in neutral and when field forces act against the rod.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Stick Open | Yes |
| Stick Closed | No |
| Stick Partially Open | Yes |
Anti-Cavitation Valve
(11, 12, 15, 16, 19, 20)
What Does It Do? This check valve allows flow from the drain to re-enter the system if it is needed, to prevent a void.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Stick Open | Yes |
| Stick Closed | No |
| Stick Partially Open | Yes |
Single Rod Cylinder
(21, 22, 23)
What Does It Do? These cylinders do the work of extending and retracting the boom, stick, and bucket curl.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Leaky Gland | Yes, during certain functions |
| Leaky Seal | Yes |
| Bent Rod | Yes |
Closed Center Plug
(24)
What Does It Do? This plug prevents flow from escaping directly to the tank.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Plug missing (open) | Yes |
Hoses & Fittings
What Do They Do? Hoses and fittings channel pressurized flow from the pump, through the system, and back to the tank.
| What Could Go Wrong? | Could This Cause A Flow Problem? |
|---|---|
| Leak/Disconnect | Yes |
| Overcrimped Fitting | Yes |
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We hope you enjoyed The Ten Step Troubleshooting Process (Excavator)
A version of this troubleshooting challenge was discussed in our feature article Mobile Hydraulics Troubleshooting - A Methodical Approach published by Fluid Power World in February, 2016. If you'd like to learn more about the TSTP, check it out.