Precision and safety
The inherent design of latest-generation plastic diaphragm check valves exhibit functionality critical to exceptional performance (see Figure 3). The plastic diaphragm double-check valve itself is typically a rubber disc with a small slit. As directional pressure in the form of a fluid or gas is applied, the disc flexes toward that flow and opens the slit, allowing for very precise movement.
More advanced diaphragm discs are composed of a latex-free silicone membrane set in a closed, stand-by position for improved positional performance.
More advanced diaphragm discs are composed of a latex-free silicone membrane set in a closed, stand-by position for improved positional performance, delivering a seal mechanism that avoids a retrograde flow even at the lowest back-flow rates of 0.1 ml/h. This feature provides several benefits:
- Protection of a flow line from back pressure caused by a pinched tube or closed roller clamp
- Avoidance of cross-contamination from one part of the line to another
- Better prevention of unwanted free flow under gravity
- Air-vent functionality for applications such as enteral feeding
A key attribute of the diaphragm is its ability to provide extremely low cracking pressure compared to other check valve types, like umbrella, duckbill, and lift check valves. An important concept in check valve performance, crack pressure defines the minimum upstream pressure at which the valve will operate. Cracking pressure ranges for the more advanced latex-free silicone membrane diaphragms are equal to or less than 12mBar (0.174 psig) for one-way check valves and 100-300 mBar (1.45-4.351 psig) for anti-siphon valves (see Figure 4).
One-way check valves, with more advanced latex-free silicone membrane diaphragms, have a cracking pressure range less than or equal to 12 mBar (0.174 psig).
Plastic diaphragm check valves also excel at removing air bubbles from their downstream flow path. Clearing bubbles from the flow path is a key concern for medical device designers when evaluating the suitability of a check valve. For example, when performing cataract surgery of the eye, an incision is made into the cornea, the lens capsule is severed, and the lens material is fragmented and aspirated by a needle. In the process of subsequent eye irrigations, it's undesirable to have air bubbles blowing into the cut-open, exposed outer layer of the cornea. The latest-generation plastic diaphragm check valves minimize the possibility of this condition (see Figure 5).
Plastic diaphragm check valves excel at removing air bubbles from their downstream flow path.
Designers have options
Plastic diaphragm check valve makers generally produce a range of options for designers, but some provide more of a custom manufacturing capability. Plastic check valves can be manufactured from ABS, SAN, and polycarbonate resins. Some check valves are DEHP and latex-free, in accordance with USP Class VI and ISO 10993 standards, can be specified to withstand EtO (Ethylene oxide) and gamma radiation, and can even be autoclavable.
Some suppliers provide a wide variety of end fitments, including single barbs, tubing pockets, sockets, and male and female luers that comply with ISO 594-1 and 594-2 standards. Sizes can be made to fit with 0.118-inch (3mm), 0.122-inch (3.1mm), 0.161-inch (4.1mm), and 0.165-inch (4.2mm) tubing IDs.
Riley Phipps is the technical and design services manager at Value Plastics Inc., a Nordson Company.
This blog originally appeared on ValuePlastics.com.