Imagine you’re running an industrial plant and you’ve got a diaphragm seal protecting a pressure transmitter. Over time, the process fluid starts leaving deposits and buildup on the membrane, causing inaccurate readings.

How do you avoid taking the whole assembly apart every time you need to clean or calibrate it?

A simple flushing ring.

In this article, we’ll walk you through what a flushing ring is, what it’s used for, how it’s installed, and the different options available. You’ll also find a video where you can see it in hand and understand its uses at a glance.

What is a flushing ring?

A flushing ring is a circular accessory designed to be installed between the process flange and the diaphragm seal of a pressure instrument.

In other words, it works like a special gasket placed between the pipeline flange and the diaphragm seal of a gauge or transmitter. The ring usually has the same diameter and bolt pattern as the flange, so it sits sandwiched in the connection without altering the normal assembly.

It’s manufactured with a defined thickness (typically around 30 mm) to house one or two lateral purge ports and to accommodate standard sealing gaskets.

The term flushing ring comes from its main purpose: flushing means washing or purging the inside of the line or the space in front of the diaphragm. In Spanish, anillo de purga describes its function perfectly: it’s a ring that allows you to purge, drain, or clean without disassembling the instrument. Its construction is simple but robust, capable of withstanding the same pressure and temperature conditions as the flange where it’s installed.

In short, a flushing ring is a passive yet extremely useful component in industrial instrumentation systems that use diaphragm seals.

flushing ring
anillo purga

What is a flushing ring used for?

A flushing ring has three main uses in industrial instrumentation:

Draining and purging the line:
It allows you to flush the process line to avoid deposits and blockages. By opening its ports, you can drain trapped fluids or inject a flushing medium that removes sediments. This is especially useful in processes with viscous, dirty, or crystallizing fluids, as it prevents buildup in the area right in front of the diaphragm.

Cleaning the diaphragm:
It makes it easy to remove deposits on the diaphragm of the seal. Through the flushing ring, you can inject a solvent, steam, or pressurized water that cleans off any buildup—without removing the transmitter. Eliminating these deposits prevents measurement drift or errors caused by accumulated dirt.

In-situ calibration of the instrument:
It enables calibration of the measurement point once the process is isolated. If you have a shut-off valve in the line and valves on the flushing ring itself, you can calibrate the transmitter in the field by injecting a reference pressure through the ring. In other words, with a flushing ring equipped with valves—and after closing the upstream process valve—you can apply a calibration pressure directly to the instrument without disassembling it, allowing you to verify or adjust the calibration in place.

In short, a flushing ring lets you drain, clean, and calibrate pressure-measurement systems easily—without removing the instrument or interrupting… (continúa tu texto y te traduzco la siguiente parte).

How is a flushing ring installed?

Installation of a flushing ring is straightforward and is done when mounting the transmitter (or gauge) with a diaphragm seal onto the process flange:

  1. Ring placement: The flushing ring is positioned between the process flange and the instrument’s diaphragm seal. Its flat faces use standard gaskets on each side to ensure tight sealing, just as if the seal were mounted directly on the flange.
  2. Alignment: The bolt holes of the flushing ring match those of the flange, allowing the mounting bolts to pass through. The ring is carefully aligned so its purge ports sit in the desired orientation.
  3. Bolt tightening: The flange bolts are tightened to the appropriate torque, clamping the flushing ring firmly between the flange and the diaphragm seal. Since the ring has the same diameter and standardized thickness, it doesn’t introduce gaps or require any special modifications.
  4. Port connection: Once installed, the flushing ring provides one or two threaded lateral ports. These ports are normally supplied in standard thread sizes (typically cylindrical BSP “G” threads) so accessories can be connected easily. If there is only one port, the ring usually includes a plug; if it has two ports, it may have plugs on both or a plug and a valve, depending on the required configuration.

It’s worth noting that the “G” thread can be installed on one or both sides of the flushing ring.

Characteristics and configurations of flushing rings

As we’ve seen, flushing rings are relatively simple components, but there are different configurations and options to match each application. Here’s a summary of the main characteristics of the flushing rings offered by Redfluid:

Flange diameters and standards

Flushing rings are manufactured to fit both metric flanges (DIN/EN standards) and imperial flanges (ASME/ANSI standards). This means there are rings available for all common nominal diameters—typically from DN25 to DN125 in European standards, and from 1″ to 5″ in American standards. Their design follows the dimensions specified in ANSI B16.5 or DIN EN 1092-1, ensuring full compatibility.
The ring thickness is usually around 30 mm (similar to an intermediate spacer) to allow proper tightening with standard gaskets.

To illustrate, here are some typical sizes of standard flushing rings:

Flange DIN (EN 1092-1)Flange ANSI (ASME B16.5)
DN251″
DN401½”
DN502″
DN803″
DN1004″
DN1255″

(Other larger nominal sizes are available on request, including DIN/ANSI flanges in bigger diameters or higher pressure ratings.)

In terms of pressure, a properly designed flushing ring withstands the same class or PN rating as the flange where it’s installed.
Redfluid’s standard models cover everything from PN10 to PN100 (equivalent to ANSI Class 150 to 600), depending on the size.

If your application requires it, we can also manufacture special rings for higher-rating flanges (for example Class 1500/2500 or PN250/PN400), ensuring full safety even in very high-pressure systems.

Materials of construction

At Redfluid we manufacture flushing rings in a wide range of special materials. The most common material is 316L stainless steel, suitable for most industrial applications thanks to its corrosion resistance. But if the process fluid is particularly aggressive or the conditions demand it, we can supply the ring in high-performance exotic alloys such as Duplex and Super Duplex stainless steels, Hastelloy, Monel, Inconel, Titanium, and others.

Purge ports and integrated valves

All flushing rings include at least one threaded lateral purge port, as mentioned earlier. This port is normally supplied closed with a screw or threaded plug to ensure tight sealing when not in use. Depending on your needs, we offer different configurations:

  • One or two ports: You can choose rings with a single lateral port (sufficient for simple purging) or with two opposite ports (recommended for flushing circuits, allowing inlet and outlet of the flushing medium). Both types install the same way and maintain full flange integrity.
  • With plugs or with valves: The standard option is to supply the ports with threaded plug screws. However, at Redfluid we also offer versions with pre-mounted valves on the flushing ring. These can be small needle valves or instrumentation ball valves mounted directly on the port. The advantage? You can open or close the purge quickly without handling plugs, and even keep a fixed drain or calibration line connected. Versions with integrated valves expand the seal system and allow maintenance to be carried out more safely and efficiently—without disassembly.

Advantages of using a flushing ring

Using flushing rings in your measurement systems with diaphragm seals can provide major benefits in maintenance, accuracy, and cleanliness:

  • Simplified and safer maintenance: Since you can clean the diaphragm or purge the line without removing the instrument, plant downtime is drastically reduced.
  • Sustained measurement accuracy: The buildup of sediments or crystallized products on a diaphragm seal can cause drift over time. By keeping the diaphragm area clean through periodic flushing, the flushing ring helps maintain the accuracy of your transmitters.
  • Longer component life: A diaphragm seal that’s regularly cleaned suffers less corrosion and fewer issues caused by solid deposits. This extends the lifespan of both the diaphragm and the internal fill fluid, delaying costly replacements.
  • Versatility and adaptability: Thanks to the wide range of configurations and materials available, flushing rings can be used across many industries and process applications.

Do you have questions or need a flushing ring for your installation?

We know that in industrial instrumentation every detail matters to keep your processes under control. If you’re working on a project where you need flushing rings, or you simply want to make sure you’re choosing the right one for your equipment, feel free to reach out.

At Redfluid we can help you select and supply the flushing ring that best fits your operating conditions: fluid type, flange diameter, material, service pressure, and more.