| Along with the mentioned main notions the following terms reflecting specific elements, objects and parameters of manufactured items are often used in valve production.
Valve type – classification unit characterized by interaction of the moving element of the gate (closing element) with the operating medium flow, determining key design features of pipeline valves. For example, gate, cock, valve etc.
Valve class – classification unit characterizing functionality of the pipeline valves, for instance, shutoff, regulating valves etc.
Valve standard size – configuration of pipeline valves regulated by the port area and nominal pressure and marked in the group main design document (main version of the product).
Valve version – configuration of a type of pipeline valves regulated, apart from the port area and nominal size, by variable data: main parts’ material, connection to pipeline, control type etc., the information of which is included into one group or basic design document. Version corresponds to a specific OKP code.
Design series – pipeline valves of similar design differing only with port areas.
Parameter series – designs of pipeline valves with different port areas, but identical nominal parameters.
Nominal parameters – operating medium pressure and temperature, indicated without taking into account tolerance deviations.
Operating medium – liquid, gas, pulp or their mixtures and other substances which are supposed to be controlled (shut off, distributed, regulated, discharged, mixed, phases separated) with the help of pipeline valves.
External (ambient) medium – atmospheric air, gas, liquid or other substances surrounding pipeline valves.
Powering medium –liquid, gas or other substances used as working media in valve actuators, that is creating permutation effort on the shutoff or regulating element.
Command medium – liquid, gas or other substances used to transfer command signals to the valve actuator.
Absolute pressure (Рабс) – pressure measured taking into account atmospheric pressure.
Positive pressure (Р) – pressure measured not taking into account atmospheric pressure – atmospheric pressure (Ра) is taken as reference zero, P= Paбс – Ра.
If Рабс > Ра the pressure Р is also called gauge pressure.
Vacuum (W) – positive difference between the atmospheric and the absolute pressures –
W = Ра – Рабс (когда Ра > Рабс). In engineering designing Pa is usually taken as equal to 1 kgf/sq.cm.
Operating temperature (Тр, ˚С) – maximum operating medium temperature in the normal course of production process without taking into consideration occasional short-term increases.
Actual length of valve (L) – linear dimension of the valve between external end planes of its mounting parts (flanges, couplings, sleeves, nipples, sockets for welding).
Overall height of valve (Н) – distance from valve body connecting sockets axis to crown of the construction (spindle or actuator) at open position of the product.
Consumption – volume or weight of operating medium flowing through the throat of the valve within a unit of time at preset parameters (pressure, temperature, density).
Hydraulic resistance coefficient – ratio of lost pressure and velocity (dynamic) pressure in the nominal (adopted) throat area.
Throat area – area formed at mutual bracing of movable and fixed elements of the gate.
Leakage – volume or weight of operating medium passing through the gate closed with the nominal pressure within a unit of time at preset parameters (pressure, temperature, density).
Air-tightness – property of connection (detachable or permanent, with movable or fixed contact) preventing leakage. Air-tightness in sealing devices is reached through creation of zero clearance between sealing parts with the help of a sealing element placed between them or due to strong contact of two sealing surfaces with the necessary effort, providing for the preset level of air-tightness, applied.
Norms of air-tightness are determined in state standard ГОСТ (%;;-93, which also establishes requirements to air-tightness tests. In accordance with the specified ГОСТ air-tightness tests should be conducted as follows:
DN
| PN
| Gate air-tightness test
| ≤ 80
| ≥ 1
| а) water – pressure 1,1х PN or
б) air with pressure 6 ± 0,5 kgf/sq.cm.
| ≥ 100
| ≤ 50
| ≤ 200
| ≥ 63
| Water – pressure 1,1 х PN
| ≥ 250
| ≥ 1
|
- Maximum testing time for gate air-tightness test
DN
| Maximum testing time, sec
| Metal-to-metal seal
| Non-metallic seal
| ≤ 50
| 15
| 15
| ≥ 65
| 30
| ≤ 200
| ≥ 250
| 60
| 30
| ≤ 400
| ≥ 500
| 120
| 60
|
- Maximum tolerated leakage values at acceptance tests for air-tightness classes
Air-tightness class
| А
| В
| С
| D
| No visible leakages
| 0,0006 cm3/min x DN (water)
0,018 cm3/min xDN (air)
| 0,0018 cm3/min x DN (water)
0,18 cm3/min хxDN (air)
| 0,006 cm3/min x DN (water)
1,8 cm3/min x DN (water)
|
Air-tightness class for shutoff valves is indicated in technical specifications for every type of valves. Leakage values correspond to the case of discharge to atmosphere. When determining leakages the nominal diameter is assumed in millimeters.
Impermeability – property of a part material characterized by absence of cracks, porosity, gaseous inclusions, through which operating medium can penetrate.
Reliability – ability of pipeline valves to perform the predetermined functions preserving the set values of operational characteristics in the necessary limits with the course of time taking into account the mode of operation, conditions of use and maintenance, as well as repairs, storage and transportation. The property is comprehensive and includes such requirements as faultlessness, durability etc. These requirements can be considered separately or be included as a certain combination to the estimation of valve or its separate assemblies and parts’ reliability.
Faultlessness – simple reliability index for pipeline valves characterizing their ability to survive continuously within some period of time or certain performance period.
Durability – simple reliability index characterizing ability of valves to survive before limit condition occurrence with necessary, determined by the established maintenance and repairs system. The indicator of durability is service life or endurance.
Working ability – a state in which pipeline valves can perform the predetermined functions.
Performance period – time of pipeline valves operation or its quantitative value measured in the number of its “closed-open” action cycles. Performance period can be continuous or with breaks, in the latter case the pooled estimate is taken into account.
Cycle – travel of the closing element from the starting position (“closed”, “open”) to the opposite one and back related to performance of the valve main function.
Service life – calendar duration of the valve operation from its beginning or resumption after a mid-life repair or overhaul to occurrence of the valve limit condition.
Endurance – performance period of the valves from the beginning of operation or its resumption after a mid-life repair or overhaul to occurrence of the limit condition stipulated in the normative and technical documents.
Limit condition – the condition of pipeline valves at which it can perform its functions, but cannot be used for further operation, which should be stopped due to unrecoverable violation of safety requirements. The limit condition can occur as the result of the preset parameters exceeding the established limits or in connection with the necessity of a mid-life repair or overhaul, as well as in connection with decline of efficiency of the valve operation.
Long-term strength – ability of the part material to retain strength at long-term stress (especially important at high temperatures).
Cycle strength – ability of the part material to retain strength at periodical stress.
Thermal shock – sudden exposure of metal to high temperature (at sudden entry of high-heat liquid, for example, heat-transfer metal, to the valve).
Thermal cycle strength – ability of material to retain strength at thermal shocks.
Inflammable, explosive or toxic medium – gas or liquid able to ignite, explode or have adverse effect on humans or animals.
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