By Murray Corporation on Jan 15, 2019 9:22:30 AM
In many common applications, you’re likely to select between two prominent types of hose clamps: the versatile, adjustable worm drive clamp and the tighter-fitting pinch clamp. To make that choice wisely, you need to understand what a worm drive clamp is and how it works.
A standard worm drive clamp consists of a slotted band of metal attached to a housing around a screw also known as a worm gear. When you turn the screw, the threads engage with the slots in the band and move it forward or backward, tightening or loosening the band around the hose.
The specific designs of housings, screws and nuts may differ slightly, but the main differences among types of worm drive clamps come down to size, primarily the width and the clamp diameter and the size of the screw. Generally, a more robust clamp suitable for use in high-pressure applications will combine a wider band with a larger diameter screw and larger housing.
Bigger is not always better, of course; the sealing force and band load of a narrow band will be greater than a wide band of the same diameter, if the screw and housing are the same – think of wrapping a piece of fishing line around your finger, compared to wrapping an inch-wide piece of ribbon. The narrower band concentrates the sealing force.
If two clamps have the same diameter, and the housing and screw are the same size but the only difference is the bandwidth, the clamp with the narrower bandwidth will generate more sealing force or band load and seal better than the clamp with the wider band.
Different Types Of Worm Drive Clamps
The standard worm drive clamp is used in a wide variety of applications. Its versatility is enhanced even further by the design variations that have been developed.
A quick release clamp is engineered with a flat band where the end of the band is not yet engaged into the screw housing. The screw swivels to let you engage the end of the band. Then you can slide the band until it fits snugly on the hose, swivel the screw downward and tighten it normally.
This design allows you to wrap the clamp around the middle of a hose or large tube or duct; with a standard worm drive clamp, you have to install it over an open end of the hose you’re fastening. It also makes for faster installation and removal.
The embossed band clamp is a cousin to the worm drive clamp. Instead of perforations, the band is embossed with peaks and or troughs that the screw engages with. Hose material can ooze through the perforations in a standard clamp, so the embossed clamp is better for applications involving hoses made of particularly soft or pliable materials.
Another way to prevent hose ooze is to use a clamp with an extended band. In this clamp type, the band is much longer than a normal worm drive clamp, and has an unperforated section that comes in contact with the hose. The perforated section of the band goes outside that, where it can engage with the worm drive.
Within the worm drive family is the constant torque, or constant tension, clamp. One common type is the SLHD (spring-loaded heavy duty) clamp. It uses washers to create a spring effect, allowing the clamp to expand and contract when used in applications that have large temperature swings.
Murray Corporation further refined constant tension clamps with their Dual Bead and Turbo Seal constant tension clamps. Each uses a shield with two beads that act as a spring that allows for expansion and contraction. The beads bite into the hose to create an O-ring effect, providing a super-sealing action. The shield also helps distribute the load generated by the clamp evenly for a secure connection.
In addition, the Turbo Seal Clamps have a special convoluted band that provides a second spring action. This allows for further expansion and contraction in challenging conditions, and provides performance that is up to 30% better than traditional constant tension clamps.
Worm Drive Clamps Versus Pinch Clamps
But all of these clamps are simply variations on a theme. The bigger decision when choosing a clamp type is worm drive versus pinch clamp.
The main difference between the two is that the pinch clamp is permanently installed with a special crimping tool. Also, pinch clamps are installed differently. They are a band with an ear, and a tool is positioned at the ear to crimp the clamp closed. The clamp is then tamper proof, but it cannot be adjusted or easily removed; it must be destroyed to remove it.
Advantages Of A Worm Drive Clamp
- Easier To Install: Unlike the pinch clamp, which needs a special crimping tool, the worm drive clamp can be installed with standard workbox tools.
Adjustable: The clamp can be tightened after installation if the fit has been affected by vibration, temperature changes, aging of the hose material or other conditions. The pinch clamp doesn’t allow for this.
Reusable: It can be reinstalled in the same application if the hose is swapped out, or placed in a different application altogether.
Disadvantages Of A Worm Drive Clamp
Limits To The Tightness Of The Seal: Because the worm drive clamp isn’t perfectly circular – the section with the screw housing is not always flat – it doesn’t provide 360 degrees of contact like a pinch clamp does. This leaves a potential leak path under the housing.
Limits To The Band Load: A worm drive clamp can only generate so much band load and tension onto the hose, depending on the housing length, screw length and screw diameter. Generally, a seamless pinch clamp will generate more band load.
Limits To How Much You Can Tighten It: You can only tighten a worm drive clamp so far; when you exceed ultimate torque, the clamp breaks.
Limits To Adjustability: If you choose a clamp with a band significantly longer than needed, you can end up with a D-shaped installation or one with a dangerous tail sticking out. Plus, you’re paying for that material that you don’t need.
Not Tamper-Resistant: The downside of the worm drive clamp’s adjustability is that even unauthorized personnel can adjust it. If you need a tamper-resistant seal, you should use a pinch clamp.
Affordable and versatile, worm drive hose clamps are used in a wide variety of situations: ducts, air-conditioner hoses, dryer vents, car engines, beverage dispensing, irrigation systems, marine usage and more. Coming in a huge variety of sizes and several different types and grades of metal, you should be able to find one just right for your needs.