Originally Published MDDI March 2005
Cover Story: Pumps and Valves
New Benefits Flow from Pumps and Valves
Top suppliers can help you ask the questions that will enable you to find the right components for your devices.
|Pumps and valves courtesy of KNF Neuberger Inc. (Trenton, NJ) and Parker Hannifin (Hollis, NH).|
Medical device manufacturers should be pumped up about cutting-edge gas- and fluid-moving components. New and soon-to-be-introduced pumps and valves feature smaller sizes and dispense volumes, higher flow rates, novel material and connection options, and dramatically reduced power consumption.
Welcome as these innovations might be, a larger menu of choices may make it harder for an OEM to zero in on the right component. According to suppliers, a key to successful pump and valve shopping is a thorough understanding of how the component will be used. Besides dispensing advice, suppliers can help by letting customers try out different options and making special products for unique applications.
Many of the new pumps and valves are variations on older ones. Take the latest version of the CeramPump, introduced by Fluid Metering Inc. (Syosset, NY). Used for dispensing in diagnostic systems, CeramPumps feature a valveless pumping concept developed to eliminate valve-related problems and maintenance. Key to valveless pumping is a ceramic piston that reciprocates to pump fluid and rotates to open and close ports, explains Herb Werner, marketing manager for Fluid Metering.
The company's new CeramPump is designed to dispense half a microliter per piston stroke. “As far as we know, there are no other piston pumps that go down that low,” says Werner.
|The CeramPump by Fluid Metering Inc. controls both the pumping and valving functions with only one moving part, a special ceramic piston (click to enlarge).|
Typically, he notes, submicroliter pumping is done by a syringe pump, which can dispense fluid in even smaller amounts than the CeramPump's 0.5-µl limit. But syringe pumps require a pair of valves to admit and discharge fluid, as well as a stepper motor for each valve. Moreover, they can't fill and dispense at the same time. So for applications that require continuous dispensing, syringe pumps often work in pairs, with one pump drawing in fluid and the other dispensing it. The bottom line, Werner says, is that medical device OEMs would need two syringes with four valves and multiple stepper motors to do what the CeramPump does with no valves and one stepper motor.
A peristaltic pump can also be used to dispense tiny amounts of fluid. Although such pumps are inexpensive, their tubing doesn't return to its original shape after each use. To prevent the drift and loss of accuracy caused by this shape change, users would have to keep replacing the tubing, Werner notes.
On the other hand, he adds, the CeramPump features a piston and liner made of a dimensionally stable ceramic material for long-term, drift-free control. “The dispense you get after a million cycles is going to be identical to the dispense you get the first day you use it,” he says.
Another possible replacement for the syringe pump is the LPV variable-volume pump from The Lee Co. (Westbrook, CT). Measuring 1.5 ¥ 5 in., the LPV features direct drive off a stepper motor. This feature enables it to be smaller than most syringe pumps that include a rack and pinion, according to Ralph Buck, Lee's product manager for inert pumps and valves.
New versions of the LPV will be even smaller, thanks to shrinking stepper-motor size. Today, the pumps are paired with motors measuring 1.8 in. in diameter. But according to Buck, new 1.1-in. motors will provide the same performance as their larger counterparts, enabling Lee to shrink the size of the entire pump package.
|The small LPV variable-volume pump from The Lee Co. features direct drive off a stepper motor, making it smaller than most syringe pumps that include a rack and pinion.|
LPV pumps are used for reagent dispensing in clinical chemistry applications. The latest versions of the pump include new seal geometries that help prevent seal damage caused by liquids prone to crystallization.
Still not satisfied, some Lee customers are looking for pumps with smaller dispense volumes. So in the next year, the firm hopes to introduce pumps capable of dispensing fluid volumes measured in nanoliters, Buck reports.
Pump manufacturers are also adding to their menus of air-moving devices. In Europe, the German division of Rietschle Thomas (Puchheim, Germany) has unveiled the Saphyr, an air pump designed to inflate the cuffs of blood-pressure devices. Rather than moving up and down, the Saphyr's diaphragm rolls in the pump's cylinder, explains David Droege, the company's product support advertising manager.
According to Droege, the rolling diaphragm pump can be made smaller than its counterparts with typical diaphragms. (The Saphyr measures 27 mm in diameter and 70 mm in length.) In addition, it can produce exact flow rates. “If you're looking for 0.95-L/min output, you can tune the pump to do that,” he says. By contrast, he notes, the flow rate of a conventional diaphragm pump might vary between 0.8 and 1.2 L/min unless a brushless dc motor powered the pump.
|(Top) The Saphyr rolling diaphragm air pump by Rietschle Thomas can be made smaller than pumps with typical dia-
phragms. (Below) Rietschle's 4002 pump has an elongated diaphragm that can produce higher flows due to increased surface area.
Another new offering from the company's German unit is the 4002. This pump's elongated diaphragm has a larger surface area than a conventional round diaphragm, Droege says. With its larger diaphragm, he adds, the 4002 can produce higher flows than a similarly sized pump with a standard diaphragm.
Small and lightweight, the 4002 was originally designed for handheld glucose monitors. The pump is also a good fit for gas analyzers and eye-surgery equipment, Droege says.
Like Rietschle Thomas, the T Squared Pumps unit of Parker Hannifin makes miniature diaphragm pumps for medical and analytical instruments. The latest offering from T Squared is the T2-06, which comes in single- and double-head configurations. The single-head version is designed for a 6-L/min flow and up to 20 psig of pressure. It has a volume of 7.73 cu in. and weighs 190 g. Slightly larger and heavier is the double-head version, which offers a flow rate of 12 L/min.
Although it fits in the palm of your hand, the T2-06 isn't as small as its predecessor, the T2-05. Nevertheless, the pump offers a combination of small size and high performance that makes it suitable for a variety of portable medical devices, according to Robert Howard, sales and marketing manager for Parker Hannifin's Pneutronics Division (Hollis, NH).
Valves Open to Change
As for valves, familiar offerings are sporting some new features. One of these is the Ultrasite from B. Braun Medical Inc. (Bethlehem, PA). The needle-free valve is designed to improve the handling and safety of intravenous devices. The valve remains closed until a syringe or IV line is attached, eliminating the need for caps or cannulas.
|Parker Hannifin's T2-06 miniature pump, although larger than its predecessor, includes features that make it suitable for portable medical devices.|
The original version of the Ultrasite is compatible with luer-lock connectors. In the past year, though, B. Braun has introduced a European version of the valve that accepts a luer slip, according to Kevin Minnich, senior strategic engineer for the company's OEM Industrial Division.
Another valve designed to provide needle-free access to IV systems is the SmartSite, developed by Cardinal Health Alaris Products (San Diego). The SmartSite features a straight-line fluid path that prevents pooling when the valve is deactivated. Made of silicone, the fluid path is virtually inert and therefore won't contaminate fluid flowing through the valve. Also notable is the SmartSite's lack of metal components that could cause a malfunction if the valve were exposed to magnetic fields from MRI equipment or other devices.
Alaris is currently working on material changes that will permit steam sterilization of the SmartSite. This will set the unit apart from most other valves of its kind, which are designed only for EtO or gamma sterilization, according to Bob Tolliver, the company's senior OEM sales manager.
For compact liquid-handling equipment, The Lee Co. offers the VHS, a solenoid valve measuring 0.22 in. in diameter by about 1 in. long. Soon, Lee plans to offer VHS valves with precision restriction devices built into their outlet ports. This will eliminate much of the valve-to-valve variation when VHS units are used as metering orifices, Buck explains.
OEMs looking for tiny fluid-handling components can also opt for Parker Hannifin's X-Valve, a two-position, three-way valve that's less than 8 mm wide. Recently, the firm introduced a nonelastomer version of the product, which can be used in situations where the valve is exposed to aggressive fluids. It is also a good choice if the cost of a valve that includes sturdy but expensive perfluoroelastomer can't be justified, says Jim Burns, engineering manager for Parker Hannifin's Pneutronics Division. Inside the nonelastomer X-Valve, a metal-on-plastic sealing design replaces the elastomer-on-plastic seal that is common in the valve industry, Burns explains.
|The Ultrasite valve from B. Braun Medical Inc. enables universal compatibility with both luer- slip and luer-lock connections.|
A variation on the X-Valve is designed for compatibility with a wide range of media used in medical instrumentation. Inside this valve, called the Liquid X, the diaphragm serves as a barrier that separates the flowing medium from the springs, actuator, and solenoid.
New versions of the Liquid X offer elastomer options for different applications. According to Howard, one version features perfluoroelastomer, which stands up to harsh fluids, while the other includes EPDM, which can handle a broad range of less-
In the coming months, Howard notes, the firm will be unveiling a new high-flow proportional valve that will be 20% larger than its current top-performing valves. But with the extra size comes a big payoff: four times the flow of current Parker Hannifin offerings, as well as 95% less power consumption. In addition, Howard says, the valve will have no magnetic signature, so it won't affect magnetic fields emanating from MRI equipment and other medical devices.
In the same time frame, Parker Hannifin will also introduce miniature and ultraminiature diaphragm pumps with no magnetic signature. These pumps will require less than 250 mW of power and produce less noise than comparable pumps now offered by the company.
The new pumps and valves “will enable OEMs to make a breakthrough in the total size of their packages by getting more performance out of their internal electromechanical components,” Howard says. “The people we're talking to about this technology are really taken aback by what we're able to do with devices this size.”
Selecting the Right Component
Are you in the market for one of the new pumps or valves? Before making a choice, consider the expected life of your device. A device expected to last only 50,000 cycles won't demand nearly as much of components as a device that's supposed to last 5 million cycles without service to pumps or valves, The Lee Co.'s Buck notes.
Buck also recommends that material compatibility be considered. “Depending on the liquids in the system, you may or may not need a chemically inert valve, and you may or may not be able to have metal in the flow path. These things will dictate a lot of the valve and pump design.”
|The George Fischer electrically actuated ball valves include features that offer manufacturers greater flexibility, such as automatic adjustment.|
Before choosing a valve, OEMs should thoroughly understand their application, according to Joel Bartholomew, B. Braun's research and development manager. Besides knowing a valve's pressure and flow requirements, Bartholomew says, OEMs should know details such as what alarms and software are installed in their device. “They should know that because they need to know what effect a valve would have on the alarms and software programming,” he points out.
When B. Braun representatives work with a valve customer, they'll often send the customer some stock valve samples that meet the pressure and flow requirements of the application. “You can talk about it all day long, but it's usually best if they have some valves that they can physically test,” says Tom Black, the company's vice president of sales and marketing.
If none of the company's products meet the customer's needs, B. Braun can redesign an existing product or make a custom valve for the application. Sometimes, though, the volumes are too low to justify the costs involved in developing a new product for a customer, Black says. In such cases, the firm's engineers might work with customers to redesign their devices so they can accept one of B. Braun's standard valves. Or if device specifications are the stumbling block, engineers can show customers how to make acceptable changes. “After talking to us, they might find out that they don't have to be as strict with the specs as they thought,” Black says. “And if they alter the specs, they might be able to use an existing valve.”
When it's time for pump shopping, consider these questions suggested by several top pump suppliers:
• How long will the pump operate? For example, says Werner of Fluid Metering, if your application is a short-term one requiring low accuracy, “you're probably going to go with a peristaltic pump. Typically, that's going to be the least-expensive option.”
• What's the cost of ownership? Some pumps may be inexpensive, but the cost of ownership should also be considered, according to Werner. “Once a product is in the field, you don't want to have to send a technician halfway around the world to work on the pump because it failed,” he says. “So you might want to buy a pump that's a little more expensive.”
• What type of motor will you need? If you're looking for something that will last for 10,000 hours, “the only choice you have is to go to a brushless dc motor,”
Rietschle Thomas's Droege says. Small motors of this type won't change the overall size of a pump package, he notes, but they'll probably last more than three times longer than other motors.
• Have you designed your system for real-world conditions? For example, Buck says, engineers might think that a system that dispenses into air need only be designed for 15-psi pressure. But what if the system gets clogged? In a case like this, system pressure might build to over 100 psi. Sometimes, Buck says, the resulting pressure buildup will dislodge the obstruction, but other times it may damage the pump or valve.
At KNF Neuberger Inc. (Trenton, NJ), pump customers sometimes evaluate several different options, according to David Vanderbeck, the company's business development manager. “They might start by picking out a product they think will be ideal for their application,” he says. “Then they may look at a pump that's one size down because they like the size of it. And they might also look at a pump that's one size bigger because they're looking for long life and they think a bigger pump will give them longer life.”
With several pumps under consideration, the designer must decide which characteristics are most and least important in a particular application. For example, Vanderbeck says, “a small pump operating fast could provide the performance that's needed. But that will be a very loud construction—it's going to sound like a buzzing bee. On the other hand, a big pump operating slowly might provide quiet performance and long life. But it won't have the size and weight that's desired for the system.”
According to Vanderbeck, more than 80% of the pumps KNF sells are custom-modified constructions. Many customers want KNF to shrink the size of one of its standard pumps but maintain the same level of performance. The company satisfies these customers by making changes such as optimizing the efficiency of the pump's diaphragm and valves.
It's not uncommon for KNF to improve a variety of pump performance measures—including flow, pressure, and self-priming capability—by 50% or more, Vanderbeck claims. The company does this by gaining a clear understanding of what's important to an application—and what's not. For instance, Vanderbeck says, flow rate could be increased at the expense of maximum pressure capability, or something else deemed noncritical in a particular situation. “It comes down to making trade-offs that sacrifice something the customer doesn't need.”
No matter what that trade-off is, one thing is clear. Good communication with your pump and valve suppliers is key to finding the best component for your device.
William Leventon is a frequent contributor to MD&DI. He is based in Somers Point, NJ.
Copyright ©2005 Medical Device & Diagnostic Industry