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Hoffman Differential Is My Mantra US Patent Design Key Ring

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Aluminum Square
-£0.70
+£16.25
+£16.25

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Style: Metal Square Keychain

Keep your keys safe and spectacular with this sturdy aluminium keyring from Zazzle. Beautifully printed on both sides, you can choose from thousands of designs, or personalise it with your own photos, text or unique designs. Label your car keys or keep a family photo of loved ones close to you at all times, these personalised keyrings are light and waterproof.

  • Dimensions:
    • Measurements: 2.25" x 2.25"
    • Depth: 0.045"
    • Weight: 0.05 oz.
  • Full-colour, full-bleed printing
  • Silver coloured metal key ring with plastic snap ring
  • Light and waterproof
Designer Tip: To ensure the highest quality print, please note that this product’s customisable design area measures 2.25" x 2.25". For best results please add 1/16" bleed

About This Design

Hoffman Differential Is My Mantra US Patent Design Key Ring

Hoffman Differential Is My Mantra US Patent Design Key Ring

Plumbers or anyone who lives in an old house with steam heating will enjoy this keychain featuring the US Patent 1777333 by William K Simpson for The Hoffman Differential Loop. The Hoffman Differential Loop, a device with no moving parts, keeps water in the boiler by making sure that under no circumstance could pressure in the boiler exceed 10 ounces higher than the return piping. It did this by bleeding pressure into the returns after 10 ounces was reached in the boiler. Thus, for example, if the boiler reached 11 ounces in it, then 1 ounce would be bled into the return pipes, since at no time could the return pipes be more than 10 ounces different than the boiler. What this means is that water would always be able to return to the boiler and steam would always flow since there was a differential pressure between the supply and return pipes. This device maintains an unvarying water line in the boiler independant of boiler pressure, which means that water in the boiler is never lowered to a point where the heat from the fire can exert a destructive influence on the boiler. Celebrate technology that is still applicable today in the home heating systems of old houses with this keychain.

Customer Reviews

4.6 out of 5 stars rating5.6K Total Reviews
4313 total 5-star reviews810 total 4-star reviews220 total 3-star reviews116 total 2-star reviews102 total 1-star reviews
5,561 Reviews
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5 out of 5 stars rating
By S.15 January 2024Verified Purchase
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Zazzle Reviewer Program
Bought this as a present for a friend and was very pleased with it. I would buy this again from zazzle. Print was very good. Happy with my purchase.
5 out of 5 stars rating
By Lesley H.9 September 2025Verified Purchase
Metal Square Keychain, 2.25" x 2.25"
First class service just what I wanted for my newly son-in-law .
5 out of 5 stars rating
By maria f.16 November 2025Verified Purchase
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Excellent work, great print. Came exactly as designed.
from zazzle.com (US)

Tags

Keychains
hoffman differential loopplumbersis my mantraplumbing technologyus patent 1777333older home steam heating systeminventor geek humourhoffman equalising loopboiler pressureinventor invention
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hoffman differential loopplumbersis my mantraplumbing technologyus patent 1777333older home steam heating systeminventor geek humourhoffman equalising loopboiler pressureinventor invention

Other Info

Product ID: 146284304125163057
Created on 27/07/2022, 2:42
Rating: G