טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHerer Shay
SubjectDevelopment of tools for evaluating water hammer solutions
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Avi Ostfeld
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Various water hammer control devices can be installed in water supply systems to prevent or reduce the extent of water hammer. These devices are present at the site and are exposed to sun and rain. Some operate under difficult conditions and work uninterruptedly, while others remain idle for long periods of time until needed. Therefore considerable importance is attached to their reliability. Generally a number of alternatives exist for installing devices of different types or for using a number of protection devices in combination. This work presents a practical and simple-to-use tool for evaluating the reliability of different combinations of devices, helping the engineer to find the optimal solution. Work includes mapping and presentation of aspects relating to reliability and maintenance of the range of water hammer control devices. The devices involved are pressure relief valves / surge anticipation valves, surge tanks, air valves and non-return valves. Experienced operation and maintenance personnel were selected and presented with a detailed questionnaire for the purpose of investigating and clarifying the various aspects and parameters relating to the reliability of the different devices. The following reliability parameters were derived: mean time between failures (MTBF); and mean time to repair/restore (MTTR). The overall availability (the ratio of the time the equipment is operational to the overall time) values for each device was calculated, taking into consideration the maintenance policy: constant control, periodic control or breakdown maintenance. Two real cases of water supply systems, in which the alternatives were different but equivalent in terms of effectiveness of protection and reduction of water hammer, were reviewed using the tool developed. The method for calculating the overall reliability of the system is based on formulas for calculating the availability of multi-component systems.

It was found that in systems that do not receive regular attention or control and in which only breakdown maintenance is observed, water hammer devices will not provide the required protection at a reasonable level of reliability. In systems subjected to periodic or annual attention, it is possible to arrive at reasonable levels of protection, to the extent of about 90% availability, although this is true only of systems having "convenient" operating conditions (in terms of type of water, operating pressures, quality of manufacturer, frequency of operation, etc.). Not surprisingly, systems that are under constant control provide the highest level of reliability. In such systems the differences, in terms of the availability between the devices, are smaller.