Electrostatic Discharge, Static Dissipation, and Hose
by Jeff Hopkins, on 2/12/20 9:00 AM
Pick the right hose and you won't worry about your fluid system getting zapped
"In fluid systems, static discharge can spell disaster."
Getting zapped by static electricity can be more than an irritation. In some fluid systems, it can be a disaster. If you are working with petroleum products, paint, lacquer, thinners and other volatile products, a spark is the last thing you want.
That's why selecting the right hose can be crucial. When some kinds of fluids flow through certain kinds of hose, a static charge can build up. The faster the flow, the faster a charge builds up. When it gets high enough, the electric charge will go right through the hose wall to ground itself on the exterior braiding or the nearest end connection.
Back when metal filters were common, that usually helped ground the charge. Today's paper and glass-fiber filters, however, tend to put even more of an electrostatic charge into whatever fluid passes through.
But there are materials that have the ability to alleviate a static electrical charge, having an electrical resistance more than 1×104 ohms but less than 1×1011 ohms. It's called static dissipative materials. Some Swagelok hoses are constructed with carbon black-filled nylon, PTFE, or PFA core material for static dissipation. The intent of a hose being static dissipative is to alleviate any static charge that may build as fluid flows through the hose. So, if your fluid system generates a static charge, you want to use a hose with a conductive metal core, or a PTFE, PFA, or Nylon core with carbon black, to dissipate static rather than discharge it through the hose’s core. Carbon allows the charge to travel to the end connection and exit safely.
Swagelok hose series electrical properties
- All metal hoses (FX, FM, FJ, FL, Convoluted Tube) – These hoses have all metal construction, with the ends welded on, and should always be considered conductive (Note that hoses with conductive cores may also be used in applications where fluid flow generates a static charge. The lower electrical resistance in a conductive core dissipates the charge more readily.)
- Fluoropolymer (PTFE) swaged hoses (T) – With the metal braid and an end connection swaged on, there is intimate contact between the metal braid, collar and end connection. They should be considered conductive, but only static dissipative when the carbon core is used.
- Fluoropolymer (PTFE) crimped hoses (B, X, S, C, J, W) – After crimping, the metal braids have an intimate contact with the collar, but the collar may not be in contact with the end connection due to the design of the collar/insert interface. These hoses have the potential to be conductive, but only static dissipative when the carbon core is used.
- Fluoropolymer (PFA) crimped hoses (U) – After crimping, the teeth of the collar bites down into metal braids, making contact between the two, however, the collar may not be in contact with the end connection due to the design of the collar/insert interface. These hoses have the potential to be conductive, but only static dissipative when the carbon core is used.
- Fluoropolymer (PTFE) crimped hoses (F, N) – These hoses are nonconductive due to the use of a nonconductive braid. The N series hose comes standard with static dissipative carbon core, and it is optional on F series hose. (Note: carbon core does not inherently make a hose conductive, but it does allow for a flow of electrons at a very slow and steady rate - a current of less than 0.00001 amps. A conductive hose has a current flow of 20-100 amps - almost 1 million times the flow. It's like comparing a geyser to a slow drip from a leaky faucet.)
All this can be very confusing, but remember, you never have to guess when it comes to product selection. We make hose right here at Swagelok Northern California. Our technicians can manufacture hose to your specifications, whether you need only one piece or hundreds. Who better to help you select the right materials than the people who will build your order?
Swagelok Northern California has a great deal of exposure to all aspects of fluid system design and engineering. Whether you have a simple question or a complex challenge, we're glad to hear from you.
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