Failure to detect low water levels in steam boilers has proven to be both costly and potentially disastrous, so the need to reliably monitor water levels in steam boilers is clear.
Reliable water level detection is vital to prevent damage to a plant and its personnel. Modern boilers are designed to provide clean dry steam and detection of incorrect water level in the drum. Too high a level can give wet steam, leading to turbine blade erosion and if the level is too low, the boiler tubes can overheat and risk explosion.
What is Hydrastep?
Hydrastep™ is an electronic gauging system which determines and displays both the water and steam level within the steam drum. It is designed to give outstanding reliability, with unparalleled fault tolerance and a fail-safe design. Trusted for more than 50 years, Delta Mobrey’s Hydrastep system overcomes problems associated with unreliable, maintenance-intensive gauge glasses.
The Hydrastep system has been around for many years before eventually evolving into the system we know today. Conductivity probe instruments such as Hydrastep were originally developed as an alternative to sight glasses for steam drums, also known as boiler drums or feed drums.
The drawbacks of sight glasses
Sight glasses are vertical columns attached to the drum with a glass window for level indication. These can be difficult to read and originally had no means of monitoring remotely. Conductivity probe instrumentation provided an alternative to this.
Later improvements to sight glasses included using refraction of a backlight, and then CCTV for remote viewing. Even so, CCTV images of sight glass level is notoriously difficult to read and brightly coloured LED displays have become the preferred solution for steam drum level indication.
Hydrastep 7 -The First Generation
Developed in the mid-1960s in conjunction with the UK’s Central Electricity Generating Board (CEGB). The Hydrastep 7 system comprised of a vertical water column mounted to the steam drum with a series of probes spaced along the column. These were linked to electronics mounted within a large floor standing cabinet with a visual display (as seen below).
Hydrastep 7 performance trials were carried out in several UK power stations from 1968 to 1972. Manufacturing commenced in 1972 with the first installations in 1973, then marketing in the United States began in 1983 with the first installation in 1984.
Hydrastep 2457 – Leaner & Cost Effective
The large cabinet mounted system was superseded by Hydrastep 2457. Manufactured in Farnborough by Schlumberger this is the earliest model with any known documentation.
Launched in 1975 as a smaller, lower cost version of the Hydrastep 7, the 2457 had local and remote displays, with relay outputs for level and alarms, but no other output to integrate to a customer’s control or monitoring system.
Hydrastep 2457 featured
- 12 electrodes
- Dual redundant drive circuitry (one circuit for odd, and one circuit for even electrodes)
- Relay outputs for trips or alarms
- Fault indication
Hydrastep 2467 – Continuous Level Output
Launched around 1985 Hydrastep 2467 responded to the need for an output to interface with control systems, so a 4-20mA current output was added to indicate level.
Both the Hydrastep 2457 and 2467 assumed the lower half of electrodes were in water with the upper half in steam and could only detect contamination of the steam electrodes. They therefore only needed a single wire connection to the lower electrodes, but a two-wire connection to the upper electrodes.
The remote level display LEDs were individually lit by drive signals from the controller, requiring cables with numerous cores.
Hydrastep 2468 – The Digital Generation
The Hydrastep 2468 was introduced in 1993 with a number of improvements, firstly it was able to detect any electrode contamination due to a two-wire connection to all the electrodes. It also offers a flexible number of electrodes with several remote display options now driven by digital communications which reduced cabling requirements.
In 1994 Factory Mutual Research produced an independent report titled “Reliability Analysis of the Hydrastep Model 2468”. It concluded that the probability of missing a trip situation was less than 1 in 300 million and that nuisance trips will be less than 1 in 10 million.
Electrodes are the key to Hydrastep’s proven reliability and saw considerable research and development in the 1990s. This resulted in a range of electrodes comprised of exotic metals and ceramics, manufactured in a highly guarded brazing method of controlled temperatures and pressure cycles.
Hydrastep 2468 features
- From 8 to 32 electrodes
- Dual redundant drive circuitry (for odd and for even electrodes) with dual power supplies
- Digital communications to numerous remote displays
- Contamination detection for ALL electrodes
Into the Future
Hydrastep has ensured plant and personnel safety for over five decades, with the Hydrastep name now synonymous with conductivity probe level measurement. Together with proven reliability and clear visual indication, Hydrastep will continue to be the ideal choice for the steam generating industry worldwide.
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About Delta Mobrey
With a proud history spanning over 100 years, Delta Mobrey Limited is a recognised global specialist in the design & manufacture of quality process instrumentation for the measurement and control of fluid and gases in all industrial plant and equipment.
Trusted Quality – Proven Value
Quality and reliability have always formed the cornerstone of the company’s success, recognised by industry with international approvals covering every aspect of our manufacturing and product portfolio, together with certifications spanning all areas of hazardous and regulated environments.
Global Team – Local Support
As a global organisation, Delta Mobrey is totally committed to delivering the best possible customer service and technical support, ensuring a lifetime value of ownership together with a flexible and responsive approach to meet each customer’s individual demands.