Pressure Balance

Meet our guest – Brennan Letkeman.

The Foreword.

Every man-made object you see around you has been designed and engineered at some point. However, we rarely take time to appreciate the brilliant designs we can’t see. Today’s article is rather different. Introducing our guest-writer Brennan Letkeman, an industrial designer and a 3D artist, who understands that the visual aspect of a product is only a fraction of what’s considered a “good design”.  – Gus Petrikas

The Article.

“Being an industrial designer is living in the Venn diagram middle of art and engineering.”
– Brennan Letkeman

When we talk about industrial design in magazines and articles we tend to talk about the exteriors of things — we talk about shape and form and material aesthetics and functions of UI buttons and so forth. Necessary things, to be sure, but perhaps a preoccupation at the expense of the guts.

And there’s almost always good design to be found in the guts of things.

Detailist Magazine Design Brennan Letkeman Pressure Balance Spool (4)

This is a pressure balance spool, and you likely used one this morning without even realising it.

Most people will go their entire life using one every day and never seeing or holding one in their hands, never knowing it exists behind their walls in quiet service of safety and comfort.

Detailist Magazine Design Brennan Letkeman Pressure Balance Spool (3)

It’s made of two pieces of chrome coated graphite that slide axially, one free floating and the other mounted into the main mixer housing with the rubber O-rings.

They’re lathed to incredibly tight tolerances to seal water and still allow the piston to slide between the two ends of hot and cold water input. Perhaps more remarkable than the design itself: we couldn’t even manufacture things to this precision a century ago, or at the very least, not at this consumer price. The engineering of the tools themselves allows engineering into the goods we use as humans, like how Apple invented ceramic sintering for the new watch bodies. There’s a progression of art that coincides with the progression of manufacturing ability.

Detailist Magazine Design Brennan Letkeman Pressure Balance Spool(1)
This was originally a luxury but quickly became common spec to outfit all showers faucets with: it’s an anti-scalding mechanism.

The whole goal is to maintain equal pressure when other water is used in a house. Namely, when a toilet elsewhere flushes and suddenly uses a large burst of cold water. In an old shower, that loss of cold pressure would suddenly feed a shower-taker with 100% hot water — not a safe or fun place to be!

So this sliding mechanism allows a loss of either pressure to cancel itself out and keep the shower a relatively consistent temperature, preventing scalding.

In practice they’re pretty dutiful little mechanisms, silently adjusting to every dip and flow of the water lines in the house. Every sink used, every toilet flushed, every dishwasher started. This little piece of free metal is keeping you comfortable and unburnt.

Detailist Magazine Design Brennan Letkeman Pressure Balance Spool (2)

And, I personally think they’re beautiful. This one sits on my desk as a little fidget toy, sliding in and out as you tumble it in your fingers. To see the holes exactly line up, imagining the water pouring through it in perfectly equal amounts. There’s an artistry to these humble pieces of metal, precise intention made by humans to help other humans live better.

So next time you take a shower, next time you turn that faucet handle, remember that there’s one of these little guys sitting just inside the wall, unseen but ever present. A tiny metal superhero of water temperature protection.

One of many hidden details in a very big world.

Find Brennan on:
His Website:
His Twitter: @Letkma


October 13, 2016 by