Tier 2 valves: Precision-flow through single-stage design

This is where flow control is the primary objective, managed through a variable-area, single-stage orifice.

At the Tier 2 level, the distinction from Tier 1 is straightforward, given that flow control is now the primary purpose rather than a secondary capability. All Tier 2 valves share one defining characteristic: the flow is regulated through a variable-area, single-stage orifice. As the valve strokes, more or less of the orifice is exposed, which varies the flow. While this might sound simple, the range of geometries that achieve this principle is surprisingly wide. And each has strengths that are suited to specific industrial applications.

Describing IMI’s Tier 2 valves as ‘open port’ is a simplification of the many different designs and geometries available. Within this level, we would include several distinct designs, each suited to different operating conditions.

Here are some examples:

In this design, the flow enters under the plug with control maintained between the plug and seat. As the plug strokes upwards, the gap between the plug and the seat increases, allowing greater flow. The contoured shape of the plug can be custom-designed to achieve different flow characteristics.

We make the small trim available in plug sizes from ¼” to 4”, with a rangeability of 30:1 to 50:1, while the larger trim is available from 1.5” to 8”, with the same rangeability.

Here, a notch is machined vertically into the plug, and control is maintained between the plug and seat. The greater the stroke, the wider the notch exposed, allowing more flow to pass through the valve. The notch can be custom-designed for different flow characteristics, and plug sizes are available from ¼” to 1”, with a rangeability of 30:1.

In this design, the plug and cage are straight, with ports machined into the cage wall. As the plug lifts, more of the port is exposed to permit flow. The ports within the cage can be shaped for specific flow characteristics. Plug sizes range from 6” to 24”, with a rangeability of 30:1 to 50:1. The ported cage is the only Tier 2 that we design that allows flow to be directed both under and over the plug, making it suitable for a wider range of conditions.

For valves with simple, straightforward functions, why does the IMI portfolio include so many different designs? To answer this, it’s important to understand how valve designs have evolved across the industry.

Different geometries have been developed to address specific applications and operating conditions. As a result, IMI offers a range of Tier 2 designs built on the same core principles, each suited to different performance requirements. Today, we continue to refine the portfolio to simplify selection and ensure the best possible fit for our customers.

That is not to say that all Tier 2 valves perform equally. Different designs can bring something unique to the table, offering genuine differentiation.

For instance, valve designs may prove to be more cost-effective if they measure 1” or less, while others are better suited to mid-range valves of between 1 and 2.5” or larger ones ranging from 3 to 26”. Moreover, some of IMI’s designs perform more effectively at fluid control while others work better with gases.

As we noted in our previous article, a Tier 1 butterfly or ball valve can provide limited flow control. However, there is a performance constraint: the rotary stroke of Tier 1 designs is shorter than the linear stroke of a Tier 2 control valve. When you require precision and enhanced flow control, Tier 2 designs are the right starting point.

The IMI valve technology portfolio provides all of the exceptional design characteristics you would expect across our Tier 2 range. But it is worth understanding where the limits lie. This provides guidance on stepping up to Tier 3.

A single-stage orifice in a Tier 2 valve means that pressure drops occur in a single step. Within the condition parameters, this works well; however, a half-open port orifice will be less precise than a drilled-hole cage with a larger flow.

The drilled-hole cage at the Tier 3 level offers finer control and reduced noise. If this is a key requirement, you should consider transitioning to a Tier 3 design.

Selecting a Tier 2 control valve is rarely about the valve alone. It is about how reliably your process performs over time, how stable control remains as conditions change, and how easily the valve can be maintained throughout its lifecycle.

Because Tier 2 valves are available in multiple geometries across the industry, it can be tempting to replace an existing design like‑for‑like. While this may seem simpler, it does not always deliver the best outcome for your process. A geometry that is well suited to one operating condition may be less effective as pressures, flows or media change.

IMI engineers take the time to understand your specific operating requirements — including flow range, pressure drop, media and control accuracy — before recommending the most appropriate Tier 2 geometry. The right selection can improve control stability, reduce wear, and help maintain consistent performance throughout the valve’s lifecycle.

This engineering‑led approach ensures that even at Tier 2, you achieve more than adequate control. You gain a solution tailored to your process that supports long-term reliability and delivers measurable value beyond the initial installation.

In the next #ChooseTheRightValve article, we will look at Tier 3, advanced control cages. At this Tier, enhanced flow control or noise reduction takes priority. A near-unlimited combination of hold patterns means these Tier 3 valves can offer a range of desired control characteristics.

Discover more about IMI valve technologies.