What is Fluid System Creep? Identifying and Preventing This Common Regulator Problem

This article and accompanying video are an excerpt from the Swagelok® Regulator Selection & Optimization Webinar presented by Swagelok Field Engineer Supervisor Jon Kestner. 

One regulator issue you may run into is creep. This is the most common issue we see in the field. Creep is the rise in outlet pressure when there's no flow. Essentially, creep is a seat leak and it is typically caused by some sort of debris or damage on the seat. 

Types of Creep

In the slide above, we see two pictures of regulators that have been returned to us. They represent debris that we sometimes see in regulator seats. There are really two types. The one here on the right looks like a tubing burr. We see that quite frequently on system startups. You can imagine a whole system is built, and maybe there's a pesky little burr still sitting in there now as it zips down the line. The space between the seat and the poppet is very small to create those pressure drops. So that burr is moving pretty fast. It's going to embed itself in that seat, causing a small leak path that is between the poppet and the seat. Even if you get some extra closing force and have a higher inlet pressure, you still might not be able to fully seal and you'll see creep.

On the bottom left, you have a situation that typically develops over time. A bunch of debris is impacting the seat and embedding itself, creating all these tiny leak paths that eventually form a seat leak. 

Why Creep is Dangerous

The reason why we worry about creep is for the protection of all the downstream components. Imagine this: There is a test bench. When the testing is over, we turn the shutoff valve, but we have creep in the regulator so there is still high pressure.

There is seat creep in this regulator. Over time, this downstream section could creep up from 100 psi to 120 psi to 170 psi to 250 psi—up and up and up. Eventually, the pressure could damage the gauges or whatever type of equipment we have here. It really could cause some problems in the system. We want to avoid that if we can, and there are some things that we can do to avoid creep.

How to Prevent Creep

There are a few ways to avoid creep:

1. Include filters. Regulators really like clean system media because they can be sensitive to debris. 

2. Add relief valves. Just downstream of the regulator, it's always a best practice to add a relief valve. 

3. If possible, shut-off upstream. It's not always possible, but shutting off upstream can take the shut-off burden away from the regulator. Regulators are not shut-off devices. They will shut off, but they're designed with pressure control in mind.

To learn more about creep, watch the Swagelok Regulator Selection & Optimization Webinar or contact us at 412.761.3212.