Control valves leakage

Pressurizing the bus enclosure A typical arrangement is shown in Figure 3I.I0. In this ease the enclosure is maintained at slightly positive pressure by continuously supplying it with dry and clean air or SF,s 1o prevent vapour condensation. Compressed iir is supplied at a pressure of 5-7 kg/cnr and passed through the air dryer and the flow control valve. The leakage, if any, is recom-... 

Seals, particularly the restricted leakage type, require auxiliary piping, control valves, and other items. If more than a suggested schematic is to be included in the vendor s scope of supply, a statement to that effect should be made. For the oil buffered systems, if a separate oil system is required, this must be stated, and it can be detailed in the accessory section with the lube system. For dry gas seals, the type of support system must be specified. The vendor s proposal should be requested to outline materials and to... 

Control Valve - Double-seated control valves are considered to pass sufficient leakage flow that equipment blocked in by such valves need not be provided with thermal expansion protection. 

Isolation A means for pressure-isolating control valves, pumps, and other piping hardware for installation and maintenance is another common application for an on/off valve. In this application, the valve is required to have tight shutoff so that leakage is stopped when the piping system is under repair. As the need to cycle the valve in this application is far less than that of a throttling control valve, the wear characteristics of the valve are less important. Also, because many are required in a plant, the isolation valve needs to be reliable, simple in design, and simple in operation. 

Plugging may be a problem in the water outlet line from the boot because of low flow rates and because solids and corrosion products tend to entrap in the boot and the water stream. The converse problem is leakage rates across the water outlet control valve exceeding the rate of water inflow into the boot. This makes maintaining boot level difficult and causes loss of product in the water stream. 

The component test loop (KVK) was provided for testing the main helium components of a nuclear process heat reactor concept (PNP) at 950 °C (max. 1050 °C for short periods). The main test components were helium to helium heat exchangers, hot gas ducts, hot gas valves, bellows, steam generators, a helium purification system, helium blowers and their acoustic emissions, helium leakage, control, and other miscellaneous systems and components. The overall operation time of the KVK amounts to more than 20,000 hours at 950 C or even higher temperatures. Its main operating parameters were ... 

Leakage past the directin control valve or changer cylinder... 

POSSIBLE CAUSES Low fluid level Suction strainer blocked Oil overheated Air entrained in fluid Leakage past direction control valve Leakage past screenchanger cylinder Pump damaged/worn REMEDY A Fill reservoir A Clean or replace A See below A Allow bubbles to subside, use antifoam A Repair or replace A Repair or replace A Replace pump... 

POSSIBLE CAUSES Faulty pressure switch Leakage past check valve Pump damaged or worn Leaking past direction control valve or screen-changer cylinder REMEDY A Replace switch A Replace pump A Replace pump A Repair or replace... 

USNRC RG 1.96 (June 1976) Design of main steam isolation valve leakage control systems for boiling water reactor nuclear power plants . USNRC RG 1.106 (March 1977) Thermal overload protection for electric motors on motor-operated valves . 

AR375 1.96 Design of main steam isolation valve leakage control systems for boiling water reactor nuclear... 

Main Steam Isolation Valve Leakage Control System (BWR)... 

D Radiological Consequences of a Design Basis Loss-of-Coolant Accident Leakage From Main Steam Isolation Valve Leakage Control System (BWR)... 

Positive-displacement pumps have an almost vertical head—flowrate curve the decline in capacity at increased pressure results mainly from increased internal leakage, a relatively small quantity in an efficient pump. It is not, however, normal to present the performance of a positive-displacement pump on a head—flowrate basis it is essentially a constant flowrate device (for constant speed), where the discharge pressure is determined by the discharge system only. Such pumps usually require a relief valve as protection against overpressure in the event of flow restriction (typically, a closed valve), and capacity is controlled by a bypass flow rather than by a series control valve. 

BWR MAIN STEAM ISOLATION VALVE LEAKAGE CONTROL SYSTEMS... 

With a variable volume controller there is a direct feedback from the air pressure in each separate room. Small variations in air leakages will result in adjusting the air control valve in such a way that the air pressure differences are maintained. Usually a smaller pressure step between rooms, e.g. 10 Pa, will be sufficient to maintain the pressure difference and airflow. The ISO standard 14644-4 mentions pressure steps of 5 - 20 Pa. However it should be borne in mind that 1 Pa (1/100.000 bar) is a very small pressure difference, which is hard to control. In the design therefore a certain margin should be observed. GMP specifies a guidance value of 10-15 Pa between rooms. 

A shutoff valve is used in each steam line outboard of the external containment isolation valve and fimctions as a backup to the isolation valve. The shutoff valve is part of leakage control system to prevent possible release of nuclear steam which could leak through the main steam containment isolation valves following a LOCA. Independent contairunent inboard and containment outboard divisions are used to establish a pressurized barrier between the containment barrier and the environs. Out leakage is effectively eliminated and in leakage is directed into the containment from the pressurized volume. Both divisions are powered from auxiliary and standby AC power. While either of the two divisions is sufficient to establish the necessary pressure barrier, both are initiated in the control... 

---