Don't let clogged air or fuel filters, voltage regulator failure, or the wrong fuel prevent your generator from doing its job.

Every day, 10 thousand truckers start their diesel engines successfully. But diesels do more than power America's extensive fleet of 18-wheelers. They are also one of the most reliable sources of emergency power for manufacturing plants, high-rise buildings, hospitals, and universities. However, the degree of dependability you can expect from such equipment comes down to one key factor: experience.

How does experience affect these two very different applications? Because truckers operate diesel engines daily, they are intimate with the unit's operational and maintenance characteristics.

More importantly, they put the engine to the test every time they use it -- under real load conditions. Running an emergency engine-generator set on a periodic basis (even at full load) does not provide you with a significant amount of operating experience.

For example, if you conduct monthly test runs of 4 hr over a 10-yr period, you'll log almost 500 hr of operational experience. Sounds good, right? Not really. When you consider it takes 200 consecutive hours or more to identify all the issues associated with power plant operation, this number becomes much less impressive.

Since an emergency generator sits idle 99.5% of the time (yet you need it to operate in less than 10 sec), it will inevitably fail at some point. So if your business requires generator runs beyond 24 hr to meet an emergency condition, it's time for you to reconsider the issues affecting its operation, including consumables and environmental/management issues.

What consumables are important? Believe it or not, simple things like fuel filters can cause big problems. The longest run we've experienced took two weeks at a multi-engine facility. The company needed continuous operation of seven out of eight engines to provide computer-processing equipment with clean power while technicians performed critical system upgrades. Within hours of start-up, we needed to change the fuel line filters. Since the designer had specified dual header filter elements fitted with a transfer valve, we could change out a complete set of filters without shutting down an engine.

Inlet and outlet fuel pressure gauges allowed us to predict when filters would clog. Without the benefits of differential pressure (dP) gauges, it's easy to imagine running until clogged filters choked off the fuel flow and the engines stall under load. Unfortunately, we did not anticipate all eight engines would require a filter change at nearly the same time over a holiday weekend. As the filter stock depleted, the rush to obtain properly sized filters escalated into a near panic situation. We had to put a lot of pressure on the vendor until he literally broke open a warehouse to resupply us.

With our filter stock replenished, we realized one of the engine gen-sets was not operating correctly. After troubleshooting the problem, we found the secondary fuel filter was not a dual-element type. It also was not fitted with dP gauges to indicate clogging. Previously, we thought someone had removed the filter element, and only an empty canister remained. This was not the case.

Although the fuel to the secondary filter was pre-filtered by the dual-header filter, years of operating as the secondary filter ultimately caused a buildup of enough debris during the extended run that the engine stalled on low fuel pressure. We temporarily removed the engine-mounted filter to get the gen-set working again. Subsequently, we rotated engine shutdowns to replace all the secondary filter elements.

Next, we looked at an undersized fuel filter head (with new filter elements installed) at another facility. In this case, the dP across the new filter elements did not decrease. This indicated piping losses were limiting the fuel supply and preventing the engine from loading to full capacity. Monthly testing had not previously revealed a fuel flow limitation because no one had ever tested the engine at full load. It was not until the staff used the engine in an emergency situation that they noticed the flow restriction.

Do you have the right fuel oil? Manufacturers design diesels to run on diesel fuel. An inadvertent delivery of gasoline (even high octane), water, or other contaminate-laden fuel significantly diminishes the diesel's ability to produce power.

One of our facilities experienced just such an event during an extended run when someone inadvertently supplied the diesel generator with gasoline. We typically test our fuel after delivery. However, during an extended run, we don't receive the results of the test before we use the fuel. What's the answer here? Use a reliable long-term fuel supplier.

One of our facilities houses large-capacity underground receiving tanks for fuel delivery. We then transfer the fuel to similarly sized supply tanks when supply levels run low. We typically maintain both the receiving and supply tank full. Consequently, we have more than 75,000 gal of underground fuel stored and ready to use. Although this appears to reflect efficiency, fuel oil that sits for several years will suffer biological contamination.

Routine engine testing does not provide significant inventory turnover of the fuel. Microorganisms that consume fuel live, breed, and die, inside your tank. When "show time" comes, filters can clog with biological waste. Fuel contamination can also cause engine sputters that result in voltage or frequency transients.

Technicians perform most fuel transfers from receiving tank to supply or day tank by automatic operation of the transfer pumps. During an extended emergency run, we found as our supply tank depleted, the automatic feature of our transfer pumps did not work. This heightened our awareness of the fuel supply system, which spurred an in-depth review of our fuel delivery system, ultimately exposing several points of potential failure that could interrupt service.

Your lube oil could become a problem. After two days into one extended generator run, the plant engineer came to me and said: "The lube oil may be running low. We're going to have to shutdown the engines to check the levels and add oil." I didn't see this as a problem, except I already had engines out of service to replace fuel filters, and the load required seven out of eight engines to be operational. Although this was not difficult to manage, I was anxious knowing that automatic load shed would start if another engine failed. A few months after the run, we had an external oil reservoir with oil level gauge installed for each engine so the staff could check oil levels while the engine is in operation.

An engine-generator set vendor came to me in the midst of one of my extended runs and said: "Your engines are rated for standby service, and you have more than 200 run hours on your lube oil. We recommend you shutdown the engines and change the oil and filter or you'll void the warranty." I easily envisioned his head on a stake.

Unfortunately, the vendor made this recommendation during a meeting in front of the CEO. Two hours later I was draining 50 gal of scorching lube oil out of the first of eight engines.

What's the lesson here? Make sure you follow the manufacturer's recommendations on the time period in between lube changes, it's usually 300 hr for prime power and 100 hr for standby service.

Don't take air intake filters for granted. We have many engine check sheets showing the air intake filter dP to rest just below 0 in. on the dial indicator where it should be. However, about a week and a half into an extended generator run at one of our facilities, the dP gauge needle suddenly rose above zero on a single filter. Within the next 8 hr, the needle traversed the dial exponentially until it began to redline at an unprecedented 10 in. dP. The air filters for the other engines also indicated an impending need for change. Once again, we found ourselves scrambling to obtain adequate filter stock, shutting down engines to swap out filters, and bringing the gen-sets back online.

It wasn't until after the run that we discovered the source of our air intake filter problem. The crankcase vents allowed the crankcase gases to vent to the atmosphere as part of normal operation.

Over the years, and particularly during the long runs, enough oil mist had clogged all of the air filters to increase the dP. Subsequently, we began a project of installing crankcase breather filters that separate oil mist and dirt from the crankcase gases before venting to atmosphere.

Upgrade your control system. Adding to the chaos of lube oil changes and fuel filter swaps, a 10-yr-old voltage regulator failed during the extended run. Failure of a voltage regulator can cause an engine gen-set to either assume more or less load& -- depending on the voltage drift. There were two options in this situation: The engine could assume enough load to trip out on overload, or the generator could run with such low voltage that it stopped being a generator and started becoming a load until it trips on reverse current. Either situation is obviously unappealing.

If such a failure occurred during routine testing, the simple solution is swapping the regulator with a new one and running the engine to set the voltage and test the paralleling features. Unfortunately, we are not set up to test an engine independently while the building is using the engines as a main power source.

Once we replaced the voltage regulator, we debated restoring the engine to service. We needed to be certain the engine would not affect the critical load if we placed it back online. With only a marginal number of engines online, we decided it was too risky to place the engine in service until the end of the extended run.

The same control system also used a myriad of 10-yr-old relays for load management. Periodically, one of these relays failed, like one controlling a priority load shed level. Imagine carrying the entire building or critical load when suddenly there are reports "the load was lost." Then, there is a frantic effort to verify if the engines are running and which load was lost.

The problem with our control system only had to happen once before we invested in a wholesale upgrade of our relays to silver-coated contacts. We also upgraded an already rigorous test program to ensure maintenance exercised and functionally tested every relay at least once a year. This is beyond the normal weekly and monthly generator test programs.

Based on our operating experience, we implemented many costly improvements to our engine-generator sets. Unless you've had an extended run to back up the cost of your modifications, these improvements may seem like a long shot. However, it is not difficult to start incorporating a phased approach.

Setting aside part of your budget for maintenance and upgrades can make a big difference when it's show time for your emergency diesel-driven generator.

Diamond is the director of engineering & property manager for the Cushman & Wakefield Greenwich Street Complex in New York.