A new, patented design from Colder Products (St. Paul, MN) eliminates both of these problems and has other advantages as well. The ChemQuik CQN08 series quick-disconnect couplings were developed forhigh-flow, ultrapure chemical applications. These couplings feature a nonspill design that allows safe, instant, spill-free, reliable line disconnects and a metal-free, spring-free flow path for smooth, unrestricted flow rates up to 40 gal/min. They provide an economical solution for minimizing downtime and reducing total maintenance costs in chemical process systems, leading to increased yield and improved operator safety.

One major adoptee of the new coupling is Ashland Specialty Chemical's fab services group (Austin, TX), which employs the component for the transfer of drummed chemicals to a day tank for subsequent use in the fab. "The spillage is the lowest of any coupling around," according to Darrell Morris, a senior equipment technician with Ashland. "It is a well-engineered product, with advantages such as its high flow rate and the ease of connecting and disconnecting." The chemicals that Ashland deploys using the coupling include sulfuric acid, hydrofluoric acid, phosphoric acid, ammonium hydroxide, and hydrogen peroxide, the technician says.

Thomas Braun, Colder's business unit manager and a copatent holder for the new coupling, addresses the question of spillage. "The amount of spillage is directly related to the amount of dead volume that is exposed to the system pressure at the instant the flow path is closed off from the fluid flow." He explains that, unlike other plastic couplings, the new design minimizes the area exposed to system pressure to a small annular area, thus minimizing spillage. An added benefit is the reduction of the annular area, which separates forces to almost zero, making the coupling quite easy to operate.

Figure 1: PTFE version of the ChemQuik CQN08 coupling on a Semco portable chemical cart.

On the semiconductor OEM side, BOC Edwards' Semco unit (Livermore, CA) uses a PTFE version of the coupling for its portable chemical cart, which blends and delivers ultrapure chemicals for various wet process applications (see Figure 1). "It provides a safe and easy means to connect and disconnect for our customers," notes Kenneth A. Johnson, Semco's director of product technology. "This coupling has the ability to connect and disconnect under pressure with no spill. We have good reports from the chemical technicians who are responsible for operating and maintaining the equipment. They really like the push-button, one-hand operation."

The couplings feature a push-button thumb latch to facilitate one-handed operation and an audible click to confirm a secure, leak-free connection. "If you want to develop a high-capacity PTFE coupling that incorporates an easy-to-use plastic thumb latch," says Colder's Braun, "then you must isolate the system pressure from generating a separating force that acts on the thumb latch. This is especially true when using weaker materials or designing a large flow coupling."

The separation force trying to push the coupling halves apart is a function of the pressure area on which the system acts at any given pressure. In addition, the pressure area increases with the square of the diameter exposed to fluid pressure. If the diameter doubles, the resulting separating force increases four times. This force must be carried by the latching mechanism holding the two coupling halves together. "Unlike common PTFE ball-and-sleeve coupling designs, typically rated at <40 psig, this pressure-balanced design allows the use of an easier-to-operate thumb latch design rated up to 80 psig," according to Braun.

When the unit is uncoupled, the fluid system pressure acts on the small annular area for biasing the coupling's two valves so they stay in the closed position in a fail-safe manner. "Upon connection, this area is isolated and effectively balanced during the joining action of the two coupling halves," explains Braun. The system pressure provides no significant separating force, except that which is applied to the small annular face area of the valves. This force, along with the spring bias, is what separates the coupling halves when the thumb latch is released. A comparison between different couplings' separation force is illustrated in Figure 2.

Figure 2: Comparison between different couplings' separation force. A lower pressure rating is desired.

Unlike poppet-style couplings that spill a significant amount of fluid when disconnected, the coupling's pressure-balanced, nonspill design permits connection and disconnection under pressure, with virtually no spillage (~0.1 ml). Braun points out that "poppet-style plastic couplings with similar flow capacity will have several milliliters of spillage versus a fraction of a milliliter for the new design."

Although metal can be used in couplings, metal corrosion within and outside of the fluid flow path could result in contamination that threatens the purity of process fluids. Some manufacturers have tried to overcome the fluid contamination problem by coating the coupling valve springs with fluoropolymers or making the spring from a low tensile strength fluoropolymer material. "Both of these are unacceptable solutions," Braun believes. "The end result is that the metal spring's coating either wears or cracks, or eventually is permeated, becomes corroded, and contaminates the fluid. The fluoropolymer spring is low force and susceptible to physical creep, resulting in unreliable sealing and valve leakage."

Because the new design locates springs outside of the flow path and hermetically encapsulates them in a fluoropolymer plastic, away from ultrapure and corrosive fluids, the risk of contamination is virtually eliminated. On the insert or plug side of the coupling, fluid flows around the edges. On the body or socket side, fluid flows through the middle. The result is that both springs are isolated by two degrees of protection from fluid contact, thus meeting stringent requirements for metallic isolation set by Intel, IBM, Motorola, Texas Instruments, and other leading chipmakers.

"Removing the metal spring from the fluid path is a major improvement for a coupling," according to Ashland's Morris. "Colder designed it so that there isn't any question of contaminating the chemicals. All the wetted materials are made of PTFE, and we also use Chemraz O-rings." (Chemraz O-rings are a product of Greene, Tweed, based in Kulpsville, PA.)

Semco's Johnson concurs. "Colder has gone through years of testing and field evaluation of the new coupling. Its key design feature is the metal-free flow path, which eliminates fluid contamination. After proving the basic design, Colder has added improvements such as keyed mating, color codes, and various fitting configurations.... The CQN08 is the best coupling I have ever used in this industry."