Edmonton Valve & Fitting Blog

Weekly posts for northern and central Alberta engineers, plant operators, and buyers.

Swagelok Monoflanges: Light, Space-Saving, and Easy to Install

by Katie Dennis, on Thu, Jun 20, 2013 @ 16:06 PM

First used in offshore oil rigs, monoflanges are finding more uses on land




Swagelok Monoflange installations at a customer site.
PDF  Download the Process Interface Catalogue

Here's an example of how the right product can make a difficult job a lot easier.

One of our customers had a reactor vessel and wanted to measure the pressure differential across the catalyst bed at various points. There are several ways to rig an assembly to do that, and Todd Scorah, one of our account managers in Fort McMurray, came up with a couple of designs using combinations of process valves. But the designs were big and bulky. They had to be permanently installed and "the piping guys were rough on them,” says Scorah.

Simple, compact assembly

Talking with the customer about the various challenges, Scorah hit on a different approach: This might be an excellent application for a process monoflange. A monoflange is basically a single, compact assembly that does the job of a more cumbersome grouping of traditional valves. Monoflanges were first developed in the 1980s by Kenmac, a company that Swagelok subsequently acquired, and they take up less space and weigh less than an assembly of standard valves. That made the product a big hit with off-shore oil rigs, where space is at a premium.

You may recall our earlier blog post about VB03 and VB04 process interface valves. The same idea applies here. The monoflange is a light, bolt-on device with a simple design, which reduces leak paths. As more land-based engineers have checked out the advantages of monoflanges, the more uses they are finding.

The monoflange-based device that Scorah suggested was small and light enough to be portable. The customer can bolt it on, take a pressure measurement, unbolt it, and move on to the next point.

The two-piece stem in our needle valves means better performance. As you rotate the handle to lower the stem, the stem rotates as well. In designs that use a single-piece stem, which means the tip of the stem continues to rotate as it makes contact with the seat. That can result in scoring, seizing, or even a weld if a high enough hardness differential is not maintained between the stem and seat. To prevent this Swagelok maintains a hardness differential of Rb 50.


Swagelok delivers a design with several advantages and of the highest quality. It takes very little torque to create a seal and hand-tightening is enough, compared to the wrench needed for a traditional gate valve.

Swagelok uses a knuckle joint on the stem to prevent stem rotation. Once the tip makes contact with the seat, it stops turning and simply moves straight down as the handle is turned. This also helps prevent misalignment, which means less worry about leaks.

Factory tested

Every monoflange is tested at the factory to ensure no visible leakage. A shell test is performed at 1.5 times maximum rated working pressure, and a seat test is performed at 1.1 times maximum rated working pressure.

And if you still find yourself comparing an assembly of three big process valves bolted together versus a monoflange, you should consider how much simpler a monoflange is to install, maintain, and that it’s self-supporting. The overall life cycle makes the monoflange a worthwhile option.

You can get specification details for our monoflanges by downloading the catalogue or from the staff at Edmonton Valve & Fitting.


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