Pumps & Systems, March 2008

Whether you are a multinational OEM or a mom-and-pop shop, pump systems are expensive and need to be protected. The protection system for the pump is a vital piece of the system and often can make or break a company financially. If a refinery on the Gulf Coast loses a pump or two, the company could lose millions. If a pump on the heating system of a store in the Maine North Woods fails, the pipes may freeze and the building could suffer serious damage. Pump operators and pump manufacturers must understand the best practices for protection and return on investment. This article examines some of these protection systems and describes the best way to install them.

Computerized Electrical Systems

More and more pumps are protected by computerized electrical systems. These systems have a multitude of features, including automatic shutoffs, wireless telemetry, dry-run features, no-flow features, pressure control sensors, temperature control sensors, etc. These systems are extremely versatile and valuable components.

The advantages of a computerized system are its adaptability and ability to be tailored exactly to the user's specifications by plugging it into a computer or changing the system's parameters. Unfortunately, they rely on energy and have to be "plugged in." Electricity is not always available (for example, in the case of a power outage), and energy is expensive. Furthermore, components-like sensors and wiring-must be installed before the pump system leaves the manufacturing floor. Once a pump system leaves its place of origin, a computerized-electrical system cannot be added.

Cutting and Soldering

Instead of ordering a computerized electrical system, some people cut and solder the components they think they might need. In this popular approach for installing a protection system, installations can be made quickly and economically. Most technicians are comfortable using torches and saws.

The advantages to this method are that technicians can install the components quickly and finish the job inexpensively. In addition, the training and skills are relatively low and easy to acquire. The disadvantages of this installation approach are that the protection systems are only as good as the components installed, and field technicians do not fully know the impact of alterations on the pump long-term. A cut and solder can change pressure tolerances and flow patterns-resulting in reduced capacity-or create a weak spot on the pipe.  

Thermal Discharge Valve

Another option for protection a pump system is a thermal discharge valve, which works based on the temperatures within the system.

Pump manufacturers and field service personnel are aware of the weaknesses in pump systems, including the internal motor and the seals inside the motor. Fortunately, the rubber compounds which now constitute the seals are stronger and more durable than they previously were. With the internal motor, if the fluid inside the pump gets too hot, so will the motor. When cool fluid comes into contact with the hot metal, it can lead to a catastrophic failure of the pump system. Since this is not groundbreaking information, why do pump systems continue to fail? Often, a full-proof safety system is not installed for the motor inside the pump.

If we use EPDM (ethylene propylene diene monomer) as our "default" rubber seal or even AFLAS (unique fluoroelastomer based upon an alternating copolymer of tetrafluoroethylene and propylene, "TFE/P")-both of which have high-end tolerances above the boiling point of water-the rubber will continue to hold shape and will not disintegrate at temperatures of 250-deg F to 450-deg F, respectively. Even if we assume that FFKM (perfluorocarbon rubber) was used (which is rated to 500-deg F), the rings will still hold. However, fluid inside the pump should never approach these temperatures in the first place. If the fluid inside a pump has reached such high temperatures, something has gone horribly wrong.

Fluid should never be allowed to approach temperature ranges that can harm the seals or the motor in a pump. However, temperature fluctuations occur routinely. A simple solution to this problem would be preventing the fluid to reach above a certain temperature from either entering a pump or staying in a pump. One option is a thermally activated valve, like a three-port discharge valve.

The heart of the three-port valve is a thermally activated actuator that opens a relief port when the fluid in the pump rises above a certain temperature. When cooler fresh fluid is brought into the valve, it reopens the outlet port, thus bringing cooler fluid into the pump. The valves have a functional range of 30-deg F to 300-deg F and a rating from 10-psi to 600-psi, and can operate in both a liquid and atmospheric medium.

This protection system has no bells and whistles, and is not as "informative" as some of the other systems mentioned (no flow rate, exact temperature, PSI, etc). However, this kind of safety system works without electricity or any outside activation process. It can also be installed without cutting or soldering, and can be "threaded" onto any pump system with any kind of thread.

Consider all the options when choosing a protection system for any new pump installation.

Anthony Truss is the market specialist for Rostra Vernatherm, 106 Enterprise Drive, Bristol, CT, 06010, 860-582-6776, Fax: 860-582-0298, www.vernatherm.com.

Tags: March 2008 Issue , Valves

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