Gate valve
The gate valve (also gas or water valve ) is a valve that is usually used to completely open or close the entire flow cross-section of a pipe . In contrast to valves , gate valves are not primarily used to regulate the flow rate and not at very high pressure. Gate valves are often used as a preliminary shut-off, i.e. to enable maintenance work on downstream valves (which take over the shut-off or regulation during regular operation).
In the case of a wedge-shaped shut-off body, contact with the sealing seat only occurs shortly before the opening is completely closed. If flowing fluids are to be shut off, the shut-off body must be guided linearly on both sides in order to fix it. At higher pressure, the pressure in the guides increases the friction and the slide becomes stiff. In the case of shut-off devices with parallel sides, the friction is always slightly increased due to the sealing surfaces sliding on each other and can be significantly increased due to contamination and corrosion. High forces may therefore be required to close the slide at high hydrodynamic pressure and to open it at higher hydrostatic pressure . A smaller shut-off valve, which opens a bypass around the actual slide valve, can be used to reduce the static pressure .
When fully open, gate valves have very little flow resistance . The space requirement of the actual slide within the pipeline is also very small.
It is operated, for example, with a slide key , a handwheel or electrically by a gear motor .
A gate valve for open channels and watercourses is called a contactor . It is also used to regulate the flow in the weir .
Gate valve for water pipes
Gate valves for water pipes are usually designed in nominal widths from 50 millimeters to several meters and in medium nominal pressure levels. The nominal pressure (PN) is usually 16 bar . Gate valves are made from stainless steel, plastic, but mostly from ductile cast iron (GGG). Compared to the previously used gray cast iron, this material offers the advantage of being more flexible and more break-resistant. Soft-seated gate valves with rubber-coated wedges are mainly used in the drinking water supply. In building installation, angle seat valves or ball valves are usually used instead of gate valves for pipelines with a diameter of up to 50 mm .
Gate valves in underground pipeline networks are usually supplied with an installation kit that enables the gate valve to be operated from the street cap . The threaded spindle is extended by means of a shaft that is designed as a square below the road surface. A slide key is placed on the square for actuation .
Gate valves are equipped with pipe threads , spigot ends , sleeves , flanges or company-specific ends at both connection ends. See also EN 736-1 "Valves - Terminology: Definition of basic types". Gate valves without connection ends can be made very flat and clamped between two flanges of the pipeline.
To protect against corrosion fittings can with an epoxy swirls sintering to GSK (Quality Association Heavy corrosion protection) or with an enamel - coating are provided. The cast shut-off wedge is protected from corrosion by a vulcanized rubber compound (W 270). The slide spindle that guides the wedge down or up is now often made of stainless steel. Other components are O-rings for sealing the spindle guide and the slide follower, which is placed on the spindle from the outside and serves as a connecting element between the slide and rods.
Metal sealing gate valves
In the case of metal-sealing valves, the sealing seat in the housing and the wedge are made entirely of metal. At the beginning of industrialization, only metallic sealing slides were used because, apart from leather, no suitable materials were available for elastic sealing.
The disadvantage of this design is the deposition of impurities in the medium (e.g. sand, lime) in the lower part of the housing (also known as the valve bag), which prevent the wedge from closing completely and can lead to leaks. Also, due to the lack of technical possibilities, the seat surfaces could not be manufactured precisely, which is why it was often not possible to achieve complete tightness even without contamination.
The advantage is the robust construction, which is what they are used for hot water pipes, e.g. B. in industrial companies, as well as for sewage systems.
Simple metal-sealing gate valves are used where absolute tightness is not important, such as in heating circuits and sewers .
If there are higher requirements for tightness and wear resistance or corrosion resistance, metallic sealing rings made of suitable material are used in the slide and sealing seat or are applied by build-up welding .
Resilient seated gate valves
Soft-seated gate valves are sealed using elastomers , which means they can also be used in gas pipes.
Resilient seated gate valves have a circumferential rubber ring which is embedded in the (wedge-shaped) closing body.
Modern soft-sealing gate valves are often equipped with a shut-off wedge rubberized on all sides, which is pressed against the sealing surface in the housing. Unevenness in the cast and minor impurities can be compensated for by pressing the rubber. If no major soiling is to be expected, it is possible to design the housing without a slider bag. In the meantime, soft-sealing gate valves are used almost exclusively in drinking and service water supplies, as they guarantee a tight seal, a long service life and largely freedom from maintenance.
Bulk gate valve
In plant construction , bulk material gate valves are used to shut off all types of bulk materials . In process engineering , bulk material gate valves are used to safely shut off and meter dry, free-flowing bulk materials, free-flowing powders and granulates, see also rotary valve .
Bulk gate valves are differentiated based on their type of actuation and shape. There are gate valves with square, rectangular and round inlets and outlets.
Manually operated slides are often used as emergency and maintenance slides to shut off free flowing bulk materials. It is operated using a handwheel , hand crank , ratchet or hand chain wheel.
Pneumatically or motor- driven bulk material slides are designed as regulating or metering slides or as working slides.
Regulating and metering slides are used where subsequent containers or conveying devices such as screw conveyors, pipe chain conveyors, trough chain conveyors are to be charged with a defined mass flow. The inlet cross-section is opened gradually or continuously in a controlled manner in order to prevent the flow of bulk material from shooting through. The slides are often equipped with a measuring system that records the position of the slide plate.
Working slide valves are used under bunkers, silos , containers, in chutes , above and below conveyor systems in order to fully open or close the existing cross-section. These slides therefore work exclusively in the mass flow range.
Needle slide
The needle valve is a special type of bulk material valve. It can serve as a gate valve for lumpy goods such as ores or aggregates when charging electric arc furnaces or as a sieve gate to hold back coarse material. From time to time the needle slide is opened in order to discharge the coarse material via a branch or distributor.
Needle valves are used for products such as broken cement clinker , limestone , slag or gypsum .
Throttle slide
Throttle slide valves are suitable for more precise adjustment of the amount of liquid flowing through. They are used particularly with large nominal sizes, for example at the bottom outlets of a dam , since valves in large dimensions are comparatively complex to design.
Hydrant valve
Between a water pipe and an underground hydrant , for example, a gate valve is installed as an initial shut-off (" slide valve "), which facilitates maintenance or later relocation of the hydrant.
When using modern "double shut-off " underground hydrants , the gate valve can be dispensed with. This results in a cost advantage during installation.
Diaphragm gate valve
The diaphragm gate valve is a special design of the gate valve. Here an elastic plastic or rubber membrane takes over the task of the slide plate. The diaphragm valve is more likely to be used in the chemical industry or process engineering due to its greater sensitivity to solids .
Gas gate valve
The gas gate valve has a purely metallic seal. Mainly fully welded constructions with a metal-sealing spindle are used.
Labelling
Gate valves on water, district heating, sewage or natural gas pipes are marked with signs to make them easier to find . These are mounted in close proximity to the fitting on pillars, on lighting masts, fences or structures. Regardless of the respective supply network, gate valves are marked with an "S", forward or hydrant gate valves with "VS" or "HS", connecting valves always with "AS". The respective nominal size (DN) is always given after this abbreviation, for example S100. The number at the foot of the "T" -shaped dividing line printed on the board indicates the distance in meters at right angles to the position of the board, the number on the side the distance to the left or right of the board. This information is important for retrieval in snow conditions, parking by cars or new road surfaces. Water is indicated by blue plates and round or oval valve covers, gas by yellow or square ones.
Web links
- Valves for gas and water distribution networks (accessed on May 20, 2017)
Individual evidence
- ↑ Handbook of water supply and wastewater technology: Volume 1: Pipe network technology , 6th edition, editor: Fritz Conradin, Vulkan Verlag (1999), p. 270