How to realize the benefits of preventive maintenance for hydraulic valves
Appeared in Plant Services on July 19, 2016
Any failure of any single component in a hydraulic system can lead to loss of productivity and potentially present a threat to the safety of workers, the public and the environment. A preventive maintenance program that is in place to keep all of those components in service can help mitigate those risks.
This article will discuss the benefits of installing a preventive maintenance program for one system component in particular—high-performance valves used in extreme or harsh conditions.
Differing perspectives on maintenance
Different organizations tend to look at the maintenance of their systems through a varied set of perspectives, depending on their product, process and organizational goals. Typically, there is a direct correlation between the product being manufactured and how maintenance within the organization is perceived. A company that uses a hydraulic system to produce high-dollar goods will generally be more proactive in its philosophy than a company that produces low-value commodity goods.
But, there is plenty of evidence to suggest that the low-value commodity producers could benefit from embracing a more proactive maintenance mindset. Let’s first take a more in-depth look at the range of existing approaches when it comes to maintaining hydraulic system valves:
The first approach is "run-to-failure" or reactive maintenance. For hydraulic systems, the benefit of this mindset is not having to spend any money on maintaining a valve until it fails. The downside of this philosophy is having to spend a great deal of money when the valve fails, most likely at a time that is tremendously inconvenient. When it does fail, production is shut down until the valve can be repaired or replaced, which usually happens on overtime. Lost production has to be made up, which usually also happens on overtime. This is the most expensive method of maintaining a hydraulic valve.
The second approach is to implement a preventive maintenance (PM) program. This method establishes time or condition intervals for performing a set list of tasks that are expected to prevent a piece of equipment from failing, and is designed to reduce maintenance costs, increase productivity, and enhance safety.
For example, an OEM valve manufacturer typically will establish guidelines for replacement or inspection of certain components, such as seals, gaskets and packing. The established interval at which service should occur for these components might be every two years (time) or 5,000 cycles (condition), whichever comes first. Some degree of flexibility is allowed for the end user to dictate when the valve will be taken out of service, as opposed to the roulette wheel approach of run to failure. Industry data shows that performing maintenance on a scheduled basis is three to five times less expensive than the same repair being made on a reactive basis.
The third approach – predictive maintenance – may be relatively new to many plant maintenance teams. Predictive maintenance utilizes a flow of information from a hydraulic system to help determine when maintenance procedures should be performed. Sensors that monitor pressure, velocity, vibration, acoustics and temperature are incorporated into the hydraulic system to gain real-time data about how a valve’s components are functioning. If a valve is operating at its design condition, it is left alone. When the performance data that is supplied by the sensors suggests a trend away from the design condition, then a work order is generated to perform a corrective action. While more costly initially than a preventive maintenance program, predictive maintenance eliminates unnecessary scheduled maintenance and its associated work interruptions.
Making the move from reactive to proactive maintenance for hydraulic systems
So how does a company that is mired in a run-to-failure mindset successfully make the transition to a more proactive approach when it comes to servicing their valves?
Communication counts. For this to happen, the benefits of the PM program have to be clearly communicated to different levels of the organization. For instance, the impact on profitability will be of prime interest to the folks in the front offices. That point may be of lesser concern to the maintenance crew who might view the installation of a PM program as heaping more work on them.
But, if it is presented to the crew that a valve PM program will reduce unexpected failures where they are asked to work on a weekend or holiday to repair or replace the valve, then that might raise their eyebrows a bit. The benefits of a valve PM program need to be communicated in language that suits the audience, whether that means talking about an improved bottom line or increased job satisfaction.
The goal is to get everyone on the same page in realizing that a PM program will benefit the company as a whole.
Leverage CMMS/database tools. As PM programs have grown in popularity, so have the tools available to help administer these programs. These typically can be run within the majority of Computerized Maintenance Management Software (CMMS) packages that are widely used. The foundation of these programs is the equipment database, which is the key component for establishing any PM program.
To create a database that can be used as the basis for a valve PM program, the first step is identifying and assigning a label for each valve in the system. Then, every valve needs to be logged into a database management program, whether that is a complex CMMS program or a self-made spreadsheet. Important information to be included is the valve type, date of installation, manufacturer, location and function.
Each valve should be given a designation and should be labeled in the field with that designation, by means of a tag, bar code or signage.
Create employee-driven procedures. The process of writing the actual PM procedure for a valve should include OEM guidelines, and more importantly, the recommendations of those employees who have hands-on experience in working on the valves. This group of people is the best resource for writing a PM procedure that fits the needs of a particular hydraulic valve. For instance, the OEM may recommend that a valve’s rod seals be replaced every three years. But, the maintenance worker who has previously rebuilt that valve and replaced those seals after only two years of service because they were failing would be able to suggest a modification to the OEM recommendation that would provide a shorter service interval.
On the other side of that coin would be an OEM recommendation that a valve piston be replaced every two years. That same maintenance person might know that the piston in question is not subjected to excessive wear and can be replaced every four years. A good PM program does not prescribe maintenance for the sake of doing maintenance. Rather, it should service the valve when it is needed, based on the operating conditions and performance history of the valve.
Besides providing the intervals for service, the procedure also needs to include a list of required parts to complete the service, any special tools that are needed, lockout/tagout requirements and the step-by-step instructions for performing the required task. Photos or video footage of the steps of the PM procedure can also be helpful. Once the procedures have been established, all maintenance department employees should be trained in the procedures, so that consistent practices are used. The actual performance of the task should be accompanied by documentation of the service that took place, noting the person performing the service, date and any relevant notes. This information should then become part of the permanent record for that valve.
Foster a culture that promotes success. For valves in particular, there is no better way of extending the period between service intervals than controlling the cleanliness of the flow media. Contamination in the form of dirt or particulate matter is the enemy of seals, gaskets, valve seats and any other wetted valve component. The particles will cause premature erosion of those parts as they travel at high speeds through the hydraulic circuit or get wedged in close tolerance areas that lead to abrasion and scoring of surfaces.
Stagnant flow areas of the valve can become clogged with contamination particles that will eventually fall loose as a mass of disastrous contamination. Good filtration practices always help, but the best way to prevent contamination is to eliminate unwanted access into the flow media. That means having a zero tolerance for leakage. If material can leak out of the system, then contamination can enter the system through that same path. An organization that allows a hydraulic leak to go unchecked is destined to have a PM program that will ultimately fail.
With a well-designed PM program in place, it is up to management to maintain the discipline to adhere to the program and to follow through on valve servicing as recommended. This is where most programs tend to fail, as old habits are hard to break. Naturally, it is much easier to leave machines running and producing dollars than it is to shut them down for a routine ounce of prevention. But, if a PM program is allowed to mature and thrive, the benefits of the program will become evident. These include decreased maintenance costs, increased productivity and enhanced workplace safety.