The Next Generation of Couplings and Disconnects

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Plunging Ahead

When considering the dry disconnects for the safe transfer of hazardous chemicals and their feedstocks, a certain technology has risen to the fore over the years: So called “bayonet-and-plunger” or “poppet” style dry disconnect coupler. The disconnects have gained acceptance because their design and operation possesses a number of benefits like a relatively little fluid loss when the coupler is disconnected, as little as 0.5 ml of fluid, or the equivalent of 1/10th of a teaspoon (approximately 0.017 of an ounce).

They are also equipped with safety locks that prevent the coupler from opening accidentally. Most brands of bayonet-and-plunger couplers are lightweight and easy to maneuver, which eliminates operational stress and strain on hoses and loading arms. Their low cost also makes them attractive to manufacturers who are looking to streamline capital expenditures and protect the operation’s bottom line.

No Jack-of-all-Trades

With all that being said, bayonet-and-plunger couplers do have a number of characteristics that prohibit them from being the absolute best technology choice in chemical-manufacturing applications. First, while an extremely small amount of fluid may be lost during disconnection, there are other coupler technologies that have been proven to lose lesser amounts of fluid. From an operational standpoint, the biggest shortfall of bayonet-and-plunger couplers is their design, which puts a number of internal parts in direct contact with the fluid as any type of flow-restriction negatively affects the production process.

For example, if a bayonet-and-plunger coupler with a 2" I.D. is installed in a 2" line and, the flow rate will actually be less than what is to be expected from a free-flow 2" line as the liquid has to work its way around the coupler parts. This may also necessitate the need for a larger-than-necessary 2.5" or 3" coupler, which can be more expensive.

Disadvantages of Bayonet Couplings

Additionally, a bayonet- and-plunger coupler’s internal components, such as springs, guides and poppets, can also create areas where the liquid can collect and nest, which makes it difficult to clear and maintain a clean pumping environment; especially when handling liquids with higher viscosities.

Bayonet-and-plunger couplers can be at a disadvantage with closed-loop fluid-transfer systems due to the number of valves deployed. At some point the closing of two valves will leave product trapped in the hose between. The pressure that is created when the downstream valve is subsequently opened has the potential to damage the coupler ahead of it.

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