There is a basic distinction between static fittings and retractable fittings. The static fittings are available as flow-through fittings, generally for by-pass or inline applications directly within the process flow, and as immersion fittings for measurements in basins, tanks or channels.

Retractable fittings – better described from a functional point of view as “sensor lock-gates” – can be used in manual or pneumatic mode to remove and service a sensor under process conditions. This can be linked with an automatic cleaning and/or calibration function. Because of the variety of production conditions, the requirements for a fitting are as diverse as they are for a sensor: Pressure and temperature, the choice of materials and above all the type and symmetry of the installation and the desired functionality, are determined by the fitting.

Modular Fittings Product Line

Even the static fittings from Knick demonstrate the exceptional flexibility and versatility with their many modular components, including different materials, process connections, connection symmetries, sealing materials, rinsing nozzles, sensor types, protective hoods, and electrolyte reservoirs.

Flow-Through Fittings

This is most common type of fitting. It is generally a by-pass model with shut-offs on the customer side for occasional sensor maintenance. For the ARF 210/215 flow-through fitting, for example, the following options are available:

  • Body material: polypropylene, PVDF, or stainless steel.
  • Process connections: DN and ANSI flanges, imperial or DIN screw fittings.
  • Connection symmetry:
    180° straight process flow or 90° angled; with or without cleaning nozzles.
  • Sealing materials:
    EPDM, FKM, FFKM (Kalrez)
  • Sensor connection:
    G1″ G3/4″ 3 x PG 13.5
  • Sensors:
    Conductivity (2 and 4 electrodes or electrodeless), pH and DO sensors, up to 3 x PG 13.5

Such a range of variations is unique, and Knick’s specialists will be happy to provide expert advice. The range also includes quite simple, but functionally well-designed flow-through cells for drinking water applications in PP (ARF 201) all the way to boiler feed water fittings in power stations (ARF 200) – all of proven Knick quality, at a reasonable price.

Immersion Fittings

Immersion fittings with immersion tubes designed for measurements in basins, tanks, and channels are fitted with an appropriate sensor insert. The ARD 220 and ARD 230 ranges of fittings have the same modular construction as the flow-through fitting described above. Pipe clamps, process flanges, and catenary suspensions are available. Various materials (plastic and steel) are available, as well as immersion tubes in variable lengths up to two meters. The ARD 230 fitting can be adapted to all types of sensor. The combination of an immersion fitting with a sensor lock-gate (Ceramat® WA160; see below) is unique.

Sensor Lock-Gates

Compared to conductivity sensors or optical sensors, electrochemical sensors entail a greater maintenance and calibration overhead. Many processes take place in closed pressurized containers or pipe circuits, and a sensor can only be removed for maintenance, cleaning, or calibration when the container is empty or the sensor is located in a separate, sealed-off bypass. This last is fundamentally unacceptable in hygienic processes. In these cases, sensor lock-gates are needed, which can be used, manually or pneumatically, to remove and maintain a sensor under process conditions. Where required, cleaning and/or calibration may be automatic.


With the launch of the Ceramat® some years ago, Knick revolutionized the world of retractable fittings. Since then, these devices have proved themselves in highly-corrosive, abrasive, and fibrous environments, and in applications prone to blockages and deposits. The actual sensor lock-gate in the Ceramat® consists of a practically indestructible, ultra-hard, highly-polished, rotating ceramic element and a corrosion-resistant, carbon-reinforced but fixed plastic outer housing made of PEEK or PVDF. Conventional stroke movements with dynamically heavily loaded O-rings are thus a thing of the past. The essential features of Ceramat® are its freedom from wear and tear and its mechanical and thermal resilience. In conjunction with an ultra-compact pneumatic drive, this fitting is completely unaffected by process conditions.

A further unique feature is that the drive can be replaced under process conditions (i.e. full media pressure). The sensor lock-gate is not only steam-sterilizable and cleanable. Cavity rinsing can be used to spray and clean all dead volumes on the outside of the ceramic element.

The hygienic design meets the standards of the IGB (Fraunhofer Institute for Interfacial Engineering and Biotechnology) in Stuttgart. All Ceramat® versions are equipped for operation with the practical multiplug, i.e. plug-and-play for rinsing, cleaning, and calibration media, including all limit switches and check valves.

Ceramat® WA 150

is compatible with a wide range of process connections and also supports the operation of pressurized liquid electrolyte sensors.

Ceramat® WA 160
Immersion Version

Many chemical reactions take place in containers in which the sensor has to be deeply immersed in the medium. However, these sensors also need regular inspection and possibly cleaning. Until now, it was necessary to use a crane or a similar lifting device to remove the whole fitting with the sensor and clean them manually. The combination of a sensor lock-gate and an immersion fitting is the answer to these process conditions. The sensor can now be withdrawn into the cleaning and calibration chamber for simple automatic cleaning, without contaminating the process with cleaning or calibration agents.


Here, Knick has consistently improved virtually all features of conventional retractable push rod fittings.

Knick has now combined the superior principle of internal O-rings with a new patented lock-gate principle.

In contrast to earlier systems, the new system has a facility for protective rinsing of the seals. Rinse water prevents any of the process medium (e.g. fibers or particles) from getting between the O-rings and the immersion tube when the sensor is moved in and out. In this way, the O-rings are subjected to much less load than with conventional retractable fittings, and the availability of the point of measurement is increased significantly.

Such a smooth, compact construction is currently unique to SensoGate®. Here again, the single central connection with the multiplug that has already proved itself on the Ceramat® provides plug-and-play installation. There are no complicated hose connections and the old tangle of hoses is replaced by “tidy” functionality. Cost savings in service and spare parts, and ease of maintenance, were top priorities in the development of SensoGate®.

The removal of the fitting, workshop time, and the replacement of wear parts were the norm with previous fittings. In contrast, the well-thought-out design of SensoGate® guarantees that the technician can reach all relevant parts as quickly as possible, on site, without having to resort to the workshop. With SensoGate®, the immersion tube ends at the piston. The two-part construction is joined with a bayonet connector. Replacement is extremely simple. In the worst case, only the process-side component needs to be replaced or renewed to save costs. SensoGate® has a completely modular design. Without any effort, a steel version can be changed to a plastic version. Retrofitting with pressurizable sensors is also possible.

The novel lock-gate principle of SensoGate® allows a greater sensor immersion depth compared to existing retractable fittings. All immersion depths can be achieved with a sensor length of
225 mm. This makes expensive 425 mm long glass electrodes redundant. Handling is easier and the likelihood of an electrode breakage is significantly reduced.


Electropneumatic Controllers

Ideally matched to the sensor lock-gates, the Unical® 9000 and Uniclean® 900 controllers provide for perfect fully automated interplay in a complete point of measurement. Highly accurate measurements can then be taken even under difficult process conditions such as high pressure, high temperatures, and high levels of impurities. When measuring in aggressive media or at high process temperatures, the electrode rests in the calibration chamber and is only briefly moved into the process for measurement. This method decisively increases the electrode life. Control is via the Protos® 3400 measuring system or directly via a DCS. Unical® and Uniclean® can be installed next to the process, even within the hazardous area.

Uniclean® 900

For safe and easy measurement even in heavily contaminated media: electrode cleaning and rinsing are performed at user-defined intervals, with cleaning fluid and/or water being pumped automatically into the calibration chamber. As the electrode does not have to be removed for cleaning, the process can continue uninterrupted. This allows problem-free measurements in a pressure tank or in the main pipe. Costly by-pass lines are eliminated and accuracy increases.

Unical® 9000

For fully automated calibration and cleaning of the electrode at user-defined intervals without interrupting the process, even for measurements within the pressurized container: two buffer solutions plus cleaning agent plus water can be automatically pumped into the calibration chamber. The expansion pumps operate without pistons or cylinders, eliminating wear and tear on moving parts. Each pump can be simply clamped onto a module holder, and the pumps are automatically recognized by the system. Only the containers need to be refilled when the automatic level display prompts for this. The multi-pump principle results in significantly reduced cleaning and buffer costs compared to a single-pump setup, and there is virtually no mixing of buffer solutions.

Fieldbus Connection

With the Protos® 3400 process analysis system, Unical® 9000 and Uniclean® 900 allow direct connection to PROFIBUS PA and Foundation Fieldbus. Together with the new ProgaLog® 3000 parameter setting and documentation tool, the system can be easily configured and documented offline on the PC.