PTS Carrier Routing Technology Comparison

Interzone, Bypass and Smart Path are the 3 most common technologies used in hospital pneumatic tube systems. How does each technology work and what are the pros and cons? This white paper examines each routing technology and outlines the best options for efficient hospital material delivery.

Carrier Routing Technology Comparison

Pneumatic tube systems use air pressure and vacuum to transport pharmaceuticals, lab specimens, blood products and other small materials between pharmacies, labs, operating rooms, emergency departments, nurses’ stations and other hospital departments. Systems are comprised of carriers, stations, steel tubing, blowers, diverters, software and a communication network.

Carriers are reusable plastic containers that hold and protect items sent through a pneumatic tube system. Carriers begin and end each delivery at a pneumatic tube station which includes a user control panel and a carrier storage bin. Carriers travel to and from stations through a network of interconnected steel tubing at speeds up to 17 miles per hour. Blowers are large fans that generate vacuum and pressure to propel carriers through the steel tubing. Diverters are switching devices that enable carriers to transition from one tube segment to another. Software selects the route for each delivery, controls station, blower and diverter mechanics and monitors carrier traffic. The communication network is used by the software to exchange information with stations, blowers and diverters.

During a typical delivery, a carrier loaded with its contents is vacuumed from a station through steel tubing and one or more diverters to a turnaround point where the carrier stops while the blower transitions to pressure.  After waiting for a moment, the carrier begins moving again under pressure through more tubing and diverters until it arrives at its destination station.

Pneumatic tube system performance is primarily judged by two measures – wait time and transaction time. Wait time measures how long a carrier waits at a station before lifting off. Transaction time measures the time from when the “send” carrier button is pressed to the time the carrier arrives at its destination station. Any delay during a carrier’s delivery not only affects that carrier’s transaction time but the wait time and transaction time of subsequent transactions. This is because carriers use shared resources while in transit. If one carrier pauses during its delivery, other carriers cannot use the tubing, diverter or other device in use by the first carrier. As such, a blower’s transition from vacuum to pressure has an adverse effect on the performance of a system since it requires a carrier to stop. The ideal pneumatic tube system minimizes the amount of time a carrier spends stopped inside steel tubing waiting for a blower or other system resource. If more than one blower is needed to complete a delivery, the stopping, waiting and restarting increase which in turn increases the overall transaction time. Not only do stopped carriers delay deliveries, they delay patient care.

As a pneumatic tube system increases in size, more than one blower is often needed to complete a delivery. In a traditional system, typically one blower supports 10 to 12 stations, so a system with 50 stations has 5 blowers. Stations are grouped into zones with one blower per zone. A 50 station system therefore is divided into 5 zones. Carriers that travel within a zone (intrazone) use only one blower. But once a carrier travels from one zone to another (interzone), additional blowers are needed to complete the delivery.

In an interzone delivery, a carrier is first vacuumed from its origin station to a turnaround point where the carrier comes to a stop while the blower switches to pressure. Once the blower goes to pressure, the carrier progresses until it reaches the outer limit of that blower’s zone at which point the carrier is deposited in an interzone pipe. After a waiting for a period, a different blower vacuums the carrier out of the interzone pipe to yet another turnaround point where the carrier waits while this new blower switches to pressure. Once under pressure, the carrier progresses to either its destination or to another interzone pipe. When properly designed, traditional systems can meet the needs of small to midsize hospitals with modest pneumatic tube transaction volume.

A system configuration known as a bypass system approaches carrier management differently than a traditional system by holding carriers and their contents in storage devices during a transaction. Storage units can hold 6 or more carriers at a time.

In this configuration, deliveries begins as with a traditional system when a carrier is vacuumed from a station. But instead of progressing to a turnaround point, the carrier is deposited into a bypass storage unit to wait while downstream tubing and diverters become available. Since bypass systems are grouped into zones with one blower per zone, once the transaction is able to resume the same blower that first deposited the carrier into the storage device vacuums it to a turnaround point. The carrier, depending on whether it is intrazone or interzone, either progresses to its destination station, an interzone pipe, or another bypass storage device.

Because of all the time spent waiting, total carrier stopped time can be significant. The term bypass is used since other more recently sent carriers can bypass the carriers in storage. This configuration inevitably increases total transaction times since carriers and their cargo must wait midstream. This waiting can mean that pharmaceuticals and specimens are left in uncontrolled areas.  During high traffic periods, carrier wait times exceed those of a traditional system since bottlenecks form in central tubing and diverter areas. Bypass systems often mask broader design shortcomings by leading users to believe the systems is performing adequately since carriers may leave their origin stations as expected. What users don’t see is the time a carrier and its cargo spend in storage.

A third system configuration called smart path eliminates the need to group stations into zones – thereby reducing stopped carrier time. In a smart path system, up to 6 blowers are linked to an array of diverters that ultimately link to as many as 72 stations so that any one blower can handle a delivery in two moves – vacuum and pressure.

With smart path, interzone delivers began the same way they do with other configurations with a carrier vacuumed from a station. The carrier progresses to a smart path turnaround point where it pauses while the blower transitions to pressure. But instead of proceeding to an interzone tube or storage device, smart path enables the carrier to continue all the way to its destination station with its original blower providing the thrust. The entire delivery is accomplished in two moves, vacuum and pressure with only one pause during the blower’s transition from vacuum to pressure resulting in the shortest possible transaction time.

For systems over 72 stations, two or more smart path arrays are combined for even great efficiency. In such a system, smart path arrays are linked with interzone pipes. Typically, multiple interzone pipes are used so that any two stations, regardless of the size of the overall system, can be linked in no more than 4 moves – vacuum, pressure, vacuum, pressure. In such a case, a carrier is vacuumed from its origin station to a turnaround point where it is then pressured into an interzone pipe. From there a second blower attached to a smart path linked to the destination station vacuums the carrier to a second turnaround point. There the blower transitions to pressure and powers the carrier to its destination. Even in the largest systems, carriers arrive after only two brief stops. This approach is the preferred configuration at hundreds of hospitals across the United States and ideal for medium to large systems with moderate to heavy transaction volume.

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Pevco Smart Path, available as an upgrade to other manufactures systems, as well as for new and existing Pevco systems, is an advanced carrier routing system that reduces transaction times while increasing system reliability by enabling one blower to handle a transaction from start to finish. For systems over 72 stations, two or more Pevco Smart Paths are combined for even great efficiency. Traditional and bypass-style systems require the use of multiple blowers to complete a delivery that Pevco Smart Path handles alone.