Monitoring and safety
A strainer housing is a pressure vessel with defined connection points. You decide which fitted valves and instruments for monitoring are installed there: magnetic rods for ferritic particles, a bursting disc for pressure relief, thermometers in a thermowell, pressure transmitters or a sight glass. We provide the nozzles in the design – otherwise welding on the pressure housing would be necessary later.
Neodymium, Ø 25 mm
DN25 to DN50
Pt100, −50 to +500 °C
DIN 43772, 1.4571
Every measuring point and every safety device needs an opening in the housing – and every opening weakens the pressure-bearing wall, which has to be calculated and executed accordingly. If the nozzle is in the drawing from the start, it is part of the strength calculation and the inspection.
If an attachment is retrofitted later, welding is required on the finished pressure vessel. That means renewed testing, renewed documentation and plant downtime. It is therefore worth providing measuring points that will only be used later – a blanked-off nozzle costs little, a subsequent modification a great deal.
Differential pressure is the most common measuring point and has a page of its own. This page covers everything else that is fitted on or in the housing.
The following parts are used regularly. Combinations are common – one housing often carries a thermometer, differential pressure measurement and drain at the same time.
Ferritic abrasion is often finer than the mesh size and would pass through the screen. Magnetic rods in the basket retain it. They are installed upright, with several side by side for larger nominal sizes – about four rods in a DN500 basket. For cleaning, they are removed together with the basket and wiped off.
Pressure relief in case the strainer clogs and the pressure upstream of the element rises to an impermissible level. One-piece, domed, opening in a star pattern, bursting element in 1.4401, vacuum-resistant. The holder is designed for PN40 to EN 1092-1. Verification to the Pressure Equipment Directive and AD 2000 Merkblatt A1.
The thermowell to DIN 43772 is welded in, and the measuring element sits inside it. This allows the thermometer to be replaced during operation without opening the strainer. Pt100 resistance thermometer class B in 3-wire connection, 6 mm sensor, or as a dial thermometer for reading on site.
If the temperature is not only to be visible but also monitored, dial thermometers with an adjustable changeover contact are available – display range 0 to 120 °C, accuracy class 2 to DIN EN 13190. The switch point can be adjusted with the rotary knob. The strainer can also be monitored digitally.
The pressure transmitter sends the operating pressure as a signal to the control system. A sight glass in the cover or shell shows whether medium is present and how far the element is clogged – with clear media often faster than any measurement.
Not every measuring point is needed straight away. Blanked-off nozzles in the right place cost little in manufacture and avoid welding on the pressure vessel and renewed testing later. We propose their position with the drawing.
The values describe the versions we usually install. Other nominal sizes, materials and measuring ranges are possible.
| Feature | Value | Note |
|---|---|---|
| Magnetic rods | ||
| Magnet material | Neodymium | high holding force, fitted in the basket |
| Diameter | 25 mm | — |
| Lengths | 100 · 200 · 600 mm | selected by basket height |
| Fastening | 2 × M8 | bolted in the strainer basket |
| Bursting disc | ||
| Design | One-piece, domed | opening in a star pattern |
| Nominal sizes | DN25 · DN32 · DN40 · DN50 | relief area 4.5 to 22 cm² |
| Bursting pressure | e.g. 25 bar g at 100 °C | set according to design |
| Bursting tolerance | 0 / +10 % | — |
| Bursting element | 1.4401 | vacuum-resistant |
| Holder | PN40, EN 1092-1 Type B1 | material 1.4571 |
| Verification | PED 2014/68/EU · AD 2000-A1 | — |
| Temperature | ||
| Measuring element | Pt100, class B (IEC 60751) | 3-wire connection |
| Measuring range | −50 … +500 °C | depending on version |
| Sensor diameter | 6 mm | insertion length to suit the housing |
| Thermowell | DIN 43772, 1.4571 | process connection G 1/2 B |
| Dial thermometer | 0 … 120 °C, class 2 | optionally with changeover contact |
Ferritic abrasion from pumps, agitators and pipelines is often finer than any sensible mesh size. Capturing it with the screen would mean filtering so finely that the pressure loss and cleaning intervals would no longer be acceptable. Magnetic rods solve this differently: they pull the magnetisable particles out of the flow, while the screen remains designed for the actual solids size. This is rarely asked for – but anyone who has needed it once almost always orders it again.
Yes. Before production starts you receive the design drawing for approval – the drawing also shows the position of all nozzles and attachments. Only once you have confirmed it does the order go into production.
Certainly. Drawings, specifications, parts lists or the data sheet of the previous strainer are the best basis. Our design engineers adopt your requirements and adapt them where manufacturing or the applicable code requires it – we agree any deviations with you beforehand.
Only if the nozzle is already there. Otherwise welding is required on the finished pressure vessel, with renewed testing and documentation. That is why, on request, we fit blanked-off nozzles at points you only want to use later.
They sit in the strainer basket and are removed together with it. The deposit is wiped off, then the basket goes back into the housing. This does not add a separate work step.
When, in the event of a fault, the strainer can clog to the point where the pressure upstream of the element rises above the permissible value – for example with positive displacement pumps without their own protection. The bursting disc then relieves the pressure in a defined way instead of loading the housing or the element. Bursting pressure and working pressure are set with a margin between them.
Because the thermowell forms the pressure-bearing wall and the sensor sits inside it. The measuring element can be replaced or calibrated without opening the strainer or draining the plant.
Yes – it is the most common measuring point on a strainer and is described on a page of its own: from simple measuring sockets and the local display to the 4–20 mA signal for the control system.
For measuring instruments we work mainly with WIKA, for magnetic rods with manufacturers of neodymium systems. If another make is specified in your plant, we fit it or provide the matching connections for a customer-supplied instrument.
All topics at a glance: Strainer options
Tell us what is to be monitored and which connections your plant specifies. We put the nozzles in the drawing – including those you will only need later.
