Hydraulic Fittings Part 1: Threads

Objectives

  • Describe threads and their components using the correct vocabulary
  • Measure unknown fitting or port threads and classify them correctly
  • Explain best practices and common mistakes in connecting threaded fittings

The Problem

A directional control valve has arrived on your test bench. You need to connect a flow meter to conduct a test, but there's a problem; which one of the fittings should you use to attach it?

Luckily, someone has taken the time to label the fittings, but without knowing which thread is used in the valve ports, how do you know which fitting to use?

The "Will It Fit?" Game

It's really tempting to start grabbing fittings from the box, and just start trying them in the port, right?

This is a terrible plan - do not do this.

Even though threads are machined metal, they are still quite delicate, and can be easily compromised. If you ruin the threads inside of this port, and that's easier to do than you might think, you'll be buying a new valve.

The only way to find the correct fitting is to measure the threads in the port in order to learn what they are, and what they require.

Some port or fitting threads can be so similar that you'll be able to partially thread them together before encountering much resistance. If you continue to force the connection, you can warp one or both sets of threads.

You may achieve a seal, but the threads will always be damaged.

If you ever need to take the connection apart, you may be unable to reconnect it again. You also have an unsafe situation where the mismatched fitting may separate under pressure.

Tools

You're going to need some tools. Some fittings manufacturers sell thread identification kits, which include thread gauges, thread profiles and calipers, as well as identification charts for some of the more common thread sizes and styles.

You'll need some version of these tools to proceed.

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We hope you enjoyed Hydraulic Fittings Part 1: Threads

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