Water level limiter
Water level limiters are used to monitor the lowest water level in a steam or hot water boiler .
If the water level falls below the lowest possible level, there is a risk of the boiler popping as a result of the smoke pipes, which are no longer cooled, or in the extreme case of the flame pipes burning through . When it burns out, the entire water content comes into contact with atmospheric pressure, i.e. H. the entire water (several tons are conceivable here) is suddenly relaxed. The massive increase in volume can cause the burner, reversible chamber door, etc., to explode or the boiler body to crack. In extreme cases, the boiler can even be catapulted out of the boiler house. Safe and reliable systems are the top priority here. The basis for the requirement for reliable water level limiters can be found in the VdTÜV code of practice “Water level 100”, in the TRD regulations (401–402, 601–604 [national regulations]) and in the EN regulations EN 12952 part 7 and 11 ( water tube boiler ) as well as EN 12953 parts 6 and 9 ( shell boiler ). As in the VdTÜV information sheet "Wasserstand 100", the requirements for the limiter device are regulated in the European regulations in parts 12952-11 and 12953-9.
functionality
"Special design" conductive water level limiters use the electrical conductivity of the boiler water to monitor the fill level . The devices are based on the principle of the Wheatstone measuring bridge . In the "special design" devices, due to the special design, the electromechanical part of the electrode (insulation, bushing, cable connection) is permanently monitored for functional reliability. A periodic self-test for loss of redundancy and a check of the relay output contacts, which intervene in the boiler protection and switch the boiler to a safe state, is also carried out in the associated evaluation device. State-of-the-art water level limiters meet the requirements for functional safety in accordance with IEC 61508 and are acc. SIL ( Safety Integrity Level ) certified.
application
"Special design" water level limiters are characterized by:
- No mechanically moving parts
- robust construction up to PN 320
- insensitive to vibrations
- durable, electrodes are not wearing parts either
- high reliability through internal monitoring
- easy handling and installation
- Highest safety standard with EC and TÜV type approval
- Certified according to SIL 3
- Approvals from numerous classification societies for ship boiler systems
- high switching point accuracy
- simple function test
This makes their preferred areas of application:
- Steam generator (shell and water tube boilers) up to PN 320
- Hot water generation systems
- in shore and ship boiler systems
literature
- GESTRA AG Bremen: GESTRA special print: The modern equipment of steam and hot water systems
- Boiler operating technology , Fritz Mayr Resch publishing house