September 4, 2016
Imagine having a friend who lived on a daily diet of greasy cheeseburgers, a six pack, and three packs of cigarettes. Their heart is straining, working twice as hard as it should be. It’s ready to blow at any moment. You’d make it a point to talk to them and recommend that they change some habits to protect their heart…
Reality is you may already have a “friend” who is mistreating their heart, and the consequences are potentially fatal. Fortunately it’s a mechanical heart that is being overworked, and the bad habits are much easier to change. That likely “friend” is probably a piping system!
Many users are simply unaware of the torture they put their pumps through day in and day out. Deadheading, lack of proper back pressure, failure to maintain prime – each of these puts unnecessary wear and tear on a pump. Unfortunately your pump may seem perfectly “healthy” as your system appears to work flawlessly day after day, leaving you unaware that unseen dangers lurk inside. The good news is that armed with just a handful of key piping system products, you can protect the heart of your pipeline and prevent system disaster.
Back pressure is essential to assure healthy pump performance. Why is back pressure so important? Think of riding a bicycle down a steep hill in the easiest, lowest gear. With no resistance, the pedals just spin needlessly. Your legs muscles get tired out, even though they aren’t accomplishing anything. Same thing with a pump; the right amount of back pressure is like selecting the right gear on a bicycle.
The simplest and most effective way to provide appropriate resistance is to install a pump back pressure valve close to the pump. Virtually any normally-closed, spring loaded back pressure valve can be used, as long as it permits sufficient flow during operations. Back pressure setting should be adjusted for optimum pump performance.
Deadhead can occur any time there’s an obstruction in the piping system. Like an artery, a filter may give no indication of pending doom until it clogs completely. If the pump tries to run in this deadhead condition for even a few minutes, the damage can be fatal.
Some pumps are equipped with an internal bypass system, but that is like putting a band-aid on a heart patient. These internal valves are subject to friction and overheating, and merely postpone the inevitable. The good news is that the same type of back pressure valve used above can be installed to perform “bypass surgery”.
The system operator has the choice of using a three-way valve, or when space permits, a two-way valve installed on a piping tee. The spring loaded valve should be set above the regular operating system pressure, so that when the line is clogged and pressure rises, valve will open a bypass and relieve the pressure on the pump. The outlet is usually piped to return liquid to the tank, so that the pump will continue to cycle normally and not run dry.
The advantage of the two-way valve is that it is installed off the main line, so that it doesn’t impede flow under normal circumstances. The three-way design is piped directly in line, which simplifies piping but creates lower flow rates downstream.
Two additional safeguards related to deadheading and other blockage problems are the pressure switch and the flow switch. A pressure switch, installed downstream of the pump, can be set to activate an alarm or turn off equipment when blockage occurs and pressure exceeds a safe point. The flow switch is ideally installed on the bypass leg, and tells the system operator that fluid is flowing in the return pipe, indicating that something has caused blockage and is creating a bypass condition. Neither switch is recommended to be used in place of the bypass valve, but rather to enhance protection efforts for the costly pump.
Pump Prime is important to maintain, to prevent the pump from overworking at start-up. Without liquid in the suction side, the pump strains to create vacuum. This strain reduces the life expectancy of the pump, making it more prone to failure under even normal use. The most effective way to ensure prime is to install a normally-closed check valve on the suction side. In this application, the check valve is referred to as a “foot” valve.
Be aware that ball checks are not effective for this role: Ball checks require back pressure to close bubble-tight, and in many systems the trapped liquid is insufficient to create a seal. Look for a diaphragm or spring-loaded check valve, which close immediately when the pump is shut off, trapping liquid and maintaining prime. It is essential that the valve close bubble-tight with no back pressure requirement.
Don’t fight the odds
Even the most carefully designed piping systems typically average at least one fatal deadhead or run dry condition per year. Consider the example cost comparison, based on a typical1.5 hp, 3-phase mag drive pump costing $1150. Add in a modest assortment of protective measures, such as a bypass valve, flow switch and a foot valve, and assume that the price goes up to $1661.
Sounds expensive, until you consider that averaging one fatal deadhead or run dry per year, that $1150 pump actually costs $4600 if you buy one per year for four years. The $1661 protected pump, by contrast, is much more likely to last four years with proper maintenance. From a lifetime cost of ownership perspective, the additional investment makes a lot of sense.
So for your own heart, diet and exercise are priceless. For the “heart” of your piping system, back pressure, bypass and prime will keep it ticking. It’s time to break some bad habits, and spend a little on pump protection to safeguard the health of your piping system.
by Rick Bolger, Plast-O-Matic Valves, Inc.