Housing and handling
A bolted cover withstands any pressure – but every cleaning costs time at the bolt circle. The quick-opening closure reverses this: loosen the nuts, swing the bolts away, cover off. Which type is possible is decided by nominal size and pressure together – not by preference alone.
Hinged eye bolts
Clamp connection to DIN 32676
DIN 444-B
Nominal size × pressure
The cover of a strainer is not opened once a year but as often as the medium requires – weekly in heavily loaded circuits. With a bolted cover, every opening means loosening the nuts one by one, putting them down and then tightening them again crosswise. This takes time, and material is lost when nuts go missing.
With the quick-opening closure, the bolts stay on the housing. They are loosened and swung away, and the cover is free. On small nominal sizes no tools are needed at all: a clamp connection is opened by hand. The limit is set by physics – the force on the cover grows with the area and the pressure.
From the classic hinged bolt to the tool-free clamp connection. Which one fits depends on nominal size, design pressure and how clean the process has to be.
The bolts sit in hinges on the housing flange. To open, the nut is loosened and the bolt is swung to the side – it stays on the strainer. The most widespread type, from DN50 up to large nominal sizes.
Instead of wings, the nut has a closed ring. A bar can be inserted through it – this allows tightening more evenly and with more control than by hand. The ring also serves as a lifting point. In stainless steel, typically M16 to M24.
The wing nut is turned with two fingers – no spanner, no tools on the strainer. The most widespread version where the strainer is opened frequently and tightening forces remain moderate. A typical case is a simplex strainer DN200 at 10 bar.
Instead of bolts through the flange, wedge-shaped clamping claws grip the cover and housing flanges from the outside. Each one is tightened with its own nut, and a circumferential safety wire keeps them on the strainer during opening. Because each claw is released individually, the closure remains manageable even on large housings – including large nominal sizes such as DN600.
One connection instead of a whole bolt circle: a ring or clamp encloses the cover flange and is tightened by hand. On the pot type strainer this is the aseptic clamp connection to DIN 32676 up to PN10, in the chemical industry the crevice-free Tri-Clamp variant. What they have in common: no tools, but a limit in nominal size and pressure.
The classic bolt circle on the cover flange. The force on the cover increases with nominal size and pressure – at some point this is the only connection that can reliably absorb it. Easier opening then comes from the lifting and swivel device instead of the closure. On smaller housings, a rectangular cover flange with only four bolts is sometimes sufficient.
The limits are not fixed catalogue values but result from the design.
| Type or example | Value | Note |
|---|---|---|
| Types and limits | ||
| Hinged eye bolts | up to large nominal sizes | standard on basket, simplex and duplex strainers |
| Eye bolts | DIN 444-B, M16 – M24 | material A2, stainless steel |
| with wing nuts | by hand | no tools on the strainer |
| with ring nuts | bar can be inserted | even tightening, also a lifting point |
| Clamping claws | individually releasable | also on large nominal sizes, secured against loss |
| Clamp connection, aseptic | DIN 32676, up to PN10 | pot type strainer |
| Clamp connection, Tri-Clamp | crevice-free | chemicals and frequent cleaning |
| Bolted | bolt circle | when no quick-opening closure can take the load |
| Rectangular cover flange | four bolts | variant for smaller housings |
| Background | ||
| Force on the cover | pressure × area | grows with the square of the nominal size |
| Consequence | more bolts or lower pressure | limit calculated for each strainer |
The force trying to lift the cover is pressure times area. At DN100 and 10 bar this is around 8 kilonewtons, at DN300 and the same pressure already over 70 – the area grows with the square of the nominal size. That is why it cannot be said that a clamp ring holds “up to 10 bar”: it holds more at a small nominal size and less at a large one. We calculate the connection for your strainer and propose the type that suits the nominal size and design pressure.
Yes. Before production starts, you receive the design draft for approval – the drawing also shows the type of cover closure. Only once you have confirmed it does the order go into production.
Gladly. 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 in advance.
That does not depend on the closure alone but on the ratio of nominal size to pressure. The force on the cover is pressure times area and grows with the square of the nominal size. On small strainers double-digit pressures are possible; on large ones the limit is reached early. We calculate it for your case.
Eye bolts with wing nuts and all clamp connections – the aseptic variant to DIN 32676 as well as Tri-Clamp. With ring nuts, a bar inserted through the ring is sufficient; a spanner set is not needed there either.
The wing nut is faster because it can be turned with two fingers. The ring nut allows a bar to be inserted so that it can be tightened more evenly and firmly – useful when the gasket needs a defined preload. The ring also serves as a lifting point.
Wedge-shaped clamping pieces that grip the cover and housing flanges from the outside and are each tightened with a nut. A circumferential wire secures them against loss. The advantage on large housings: each claw is released on its own instead of working crosswise around a whole bolt circle.
Usually yes, but it is work on a pressure vessel: the cover flange is adapted, the bolt hinges are welded on, followed by testing and documentation. If a strainer replacement is due anyway, it is worth checking whether a new strainer is more economical.
Graphite with tanged steel insert is designed for repeated opening as long as the sealing face stays clean. For very frequent changes, elastomer or PTFE gaskets are more suitable – the choice also depends on medium and temperature.
The closure keeps the cover shut; the swivel device carries it. Large nominal sizes need both: hinged eye bolts for quick release and a hinge so that the heavy cover does not have to be lifted off.
All topics at a glance: Strainer options
Tell us the nominal size, design pressure and how often the strainer is opened – this determines which type can take the load and where the limit lies.
