Mechanical Troubleshooting: Chapter 2
Troubleshooting Static Machine Components
In this module, we will learn about the failures of static components in a machine. We’ll also learn about how to troubleshoot these failures. Skip to quiz!
Static Machine Components
A mechanical system consists of stationary and moving components. Some of the stationary components that are part of a mechanical system are:
Mechanical seals, and
Valves.
Let’s look at each of them.
Mechanical Seals
Mechanical seals are leakage control devices used in mechanical systems. Mechanical seals prevent fluids, like water or oil, used by a machine from leaking into the external environment. For example, seals on a pump prevent the leakage of liquids.
Mechanical seals come in various forms. These include:
Spring seals,
Multi-spring seals,
Metal bellows seals, and
Cartridge seals.
Considering that there is more than one type of seal, it’s essential to identify their best application. Most seal failures occur by selecting the wrong seal for the application. So, we should always follow manufacturer recommendations to select a seal type.
Installing a seal in the wrong direction is another common cause of failure. Improper installation and mishandling of mechanical seal parts can cause chips and cracks in a seal ring.
A mechanical seal might fail due to poor lubrication, or no lubrication at all. When there is no liquid around a seal, it will increase the temperature inside a system. This rapid increase in temperature can damage o-rings or rubber on the seal.
A change in operating conditions may affect the performance of a mechanical seal. For example, high-pressure levels inside a pump can potentially cause parts of a seal to break off.
Now that we know the reasons for failure, let’s learn how to identify seal failures. Most seal failures are easy to identify visually. Common signs of seal failures are:
Deep grooves on a seal face,
Cracked seal face, and
Uneven wear tracks.
When you start noticing deep grooves on a seal face, inadequate lubrication may be to blame. However, these deep grooves could also be caused by abrasive materials present in the fluid used in a pump. When abrasives are embedded in the soft face of a seal, it forms a groove on the seal.
To troubleshoot this issue, flush the seal using proper lubricant. Consider using seal face materials that can withstand abrasive materials in the fluid carried by a pump.
Thermal shock and mechanical seal impact are two reasons a seal face can fracture or crack. To troubleshoot this failure:
Avoid uneven or over-tightening of seals, and
Eliminate the cause of shock or impact, like misalignment of a shaft.
An even wear track on a seal face usually indicates good contact between the mating seal rings. An uneven wear pattern will usually indicate that a seal ring is distorted due to over tightening, clamping, or excessive pressure.
Other culprits for an uneven wear pattern could be elevated temperatures. We always need to review installation guidelines, techniques, and current operating conditions for the proper running of a seal.
Apply a small amount of grease to the seal and the area of the shaft in contact with the seal. Orient your seal the same way as the initial install. The last step involves the actual pressing-in of the seal.
Valves
Many factors can cause valve failure. Some of the more prominent causes include:
Worn elastomers and seat seals,
Debris in a pipeline,
Operating in excessive high-temperature situations, and
Improper valve installation, maintenance, and assembly.
Failing valves will emit warning signs at the first hint of trouble. For example, failing check valves will start to vibrate and even lose some internal parts when problems arise.
Failure of a valve can be identified visually. For example, we can notice too little or too much gas coming out of our gas stove if the gas valve is failed.
Valve failures are caused by damage to the individual components of a valve. The possible causes of component failure are:
Damage to the valve body or valve seat,
Actuator failure,
Coil burn out, and
Damaged seals.
Let’s look at each of them.
Valve seats and valve bodies can corrode over time if there is debris inside a pipe. We can notice a hint that a valve is corroded if there is no water coming out of our tap. To troubleshoot this, we need to clean the valve parts and ensure the pipes are clean too.
Actuators facilitate the movement of valve components, enabling a valve to open and close as needed. If we notice that a valve is not opening or closing automatically, there could be actuator failure.
Common issues in an electric actuator may include motor failure or major electrical issues. The limitation of the DC system made it challenging to distribute power in rural areas. This is why, eventually, AC became the new standard for electricity in the US in the late 1800s. After 1965, wires were grounded to direct stray electrical currents back into the ground to create a safer environments.
Recall that a solenoid valve is actuated using a solenoid coil. If our solenoid valve stops working, the possible cause could be coil burnout. A symptom of coil burnout is burn marks on a coil.
There are several causes of a burnt coil in a solenoid valve. They include:
Wrong voltage, and
A short circuit.
We need to check the voltage signal using a multimeter to troubleshoot this issue.
A valve doesn't shut off or leak if a seal is damaged or worn. Recall that seals prevent the fluid used by a machine from leaking into the external environment. If a valve is leaking, then the possible cause of the valve malfunction is a damaged seal.
We need to follow general guidelines to troubleshoot valve failure once it has been identified. The first step is to identify the location of valve failure.
After identifying the issue, we need to take necessary troubleshooting steps to solve the issue further. We need to ensure appropriate spare parts are on hand before removing a valve from service.
If it is necessary to remove a valve from piping, we need to follow the appropriate procedure. This includes:
Disconnecting the electric supply, and
Lockout Tagout.
Recall that lockout tagout is a procedure used to make sure that equipment is shut down and tagged before performing maintenance. It’s used to prevent people from working on machines that may injure them.
After a system is shut down completely, we can start disassembling the valve from the pipe. We need to follow proper disassembly and maintenance procedures to resolve the issue. Then, we need to re-install the valve into the piping with correct electrical connections.
For example, to resolve the issue of coil burnout, we need to check the solenoid valve coil voltage specifications. If the voltage is not in range, then we need to change the coil. Install a new coil thats voltage requirements are in line with our power source.
If a valve is damaged, we need to replace the valve.
The valve on the main supply line is closed before replacing the main shut-off valve. e need to actuate and test the valve to ensure proper function. Monitor valves during an initial run to ensure the replaced valve is operating correctly.
Mechanical seals fail because of:
Selecting the wrong seal,
Installation error,
Lack of lubrication, and
Improper operating conditions.
Valves fail because of:
Damage to a valve body or valve seat,
Actuator failure,
Coil burn out, and
Damaged seals.
We need to troubleshoot these issues to avoid system damage.
Question #1: What is the function of a mechanical seal?
They regulate the flow of fluid
They prevent fluid used by a machine from leaking into the external environment
They ensure no debris in the pipeline
They provide cooling to the machine
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Answer: They prevent fluid used by a machine from leaking into the external environment
Mechanical seals prevent fluids, like water or oil, used by a machine from leaking into the external environment.
Question #2: What is the first step while installing a mechanical seal on a machine?
Pressing the seal
Lubricating the seal
Ensuring no debris in the pipeline
Provide cooling to the machine
Scroll down for the answer...
Answer: Lubricating the seal
The first step of installing a seal is lubricating it. We need to apply a small amount of grease to the seal and the shaft area in contact with the seal.
Question #3: What are the causes of valve failure? (Select all that apply)
Improper pipe material
Debris in a pipeline
Improper valve installation
Operating in excessive high-temperature situations
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Answer: Debris in a pipeline
Improper valve installation
Operating in excessive high-temperature situations
Some of the causes of valve failure include:
Worn elastomers and seat seals,
Debris in a pipeline,
Operating in excessive high-temperature situations, and
Improper valve installation, maintenance, and assembly.
Question #4: Which components of a valve fail due to corrosion? (Select all that apply)
Valve body
Solenoid coil
Valve seat
Valve handle
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Answer: Valve body
Valve seat
Some of the causes of valve failure include:
Foreign or abrasive debris in a pipeline,
Material incompatibility with the product being processed, and
Temperatures or pressures outside the designed operating parameters.
Question #5: How do we identify solenoid coil failure in a valve?
Sudden change in valve pressure
From the slow opening of a valve
Measuring coil temperature
Locating burn marks on a coil
Scroll down for the answer...
Answer: Locating burn marks on a coil
A symptom of coil burnout is burn marks.
Question #6: What is a way to protect ourselves and avoid electrical risks while troubleshooting a valve? (Select all that apply)
Stand right underneath power lines
Lockout Tagout
Use damaged equipment
Disconnecting electric supply
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Answer: Lockout Tagout
Disconnecting electric supply
If it is necessary to remove a valve from piping, we need to follow the appropriate procedure. This includes:
Disconnecting the electric supply, and
Lockout Tagout.