| The term «pipeline valve» is understood as a device mounted on pipelines, units or vessels and designated to control (shut off, distribute, regulate, discharge, mix or separate phases) flows of operating mediums (liquid, gaseous, gas-liquid, powdered, suspension etc.) by change of passage area.
Pipeline valves are characterized by two main parameters:
- Port area (nominal size) and
- Nominal pressure.
Port area (nominal size) (Dу or DN) is a parameter applied for pipeline systems as a characteristic of attachable parts, for example, pipeline junctions, fittings and valves. Port area (nominal size) is approximately equal to the inner diameter of the attachable pipeline in millimeters. The values of port areas must correspond to the numbers of parameters series, determined in ГОСТ 28338-89 (total 50 numbers from 205 to 4000).
Table 6
Values of port areas (nominal sizes) under ГОСТ 28338-89
2,5
| 40
| 350
| 2000
| 3
| 50
| 400
| 2200
| 4
| 63*
| 450
| 2400
| 5
| 65
| 500
| 2600**
| 6
| 80
| 600
| 2800
| 8
| 100
| 700
| 3000
| 10
| 125
| 800
| 3200**
| 12
| 150
| 900
| 3400
| 15
| 160*
| 1000
| 3600**
| 16*
| 175**
| 1200
| 3800**
| 20
| 200
| 1400
| 4000
| 25
| 250
| 1600
| | 32
| 300
| 1800
| |
*- tolerable for hydraulic and pneumatic devices
** - not tolerable for general purpose valves
Port area or nominal size is marked using Dу or DN designation and the value chosen from the series. For example, port area (nominal size) of 200 should be marked as follows: Dу 200 or DN 200.
Nominal pressure (Ру or PN) is the highest positive operating pressure under the operating medium temperature of 20 ˚С, at which the predetermined service life of pipeline junctions and valves with fixed dimensions grounded on stress calculation given the chosen materials and their strength properties under the temperature of 20 ˚С is guaranteed.
ГОСТ 26349-84 determines the parameters series of nominal pressures including 27 parameters from 0.1 to 1,000 kgf/sq.cm. (Table 7). Nominal pressures under 0.1 kgf/sq.cm. should be chosen from R5 series, and those above 1,000 kgf/sq.cm. should be chosen from R20 series according to ГОСТ 8032-56.
As against the nominal pressure test and operating pressures are distinguished.
Test pressure (Рпр) is the positive pressure at which hydraulic strength and leak testing of valves and pipeline parts with water under the temperature between 5 ˚С and 70 ˚С, if the specific value of the temperature is not indicated in the normative and technical documents, should be conducted.
Operating pressure (Рр) is the highest positive pressure at which the predetermined operational mode for valves and pipeline parts, which implies the set operating temperature, is guaranteed. The medium temperature should be assumed as equal to the temperature at which continuous service of the product takes place not taking into account short-term fluctuations specified as tolerable in the respective normative and technical documents.
Operating pressures are equal to nominal ones for carbon steel valves under medium temperature from -20 to + 200 ˚С, for grey cast iron valves – from -15 to +120 ˚С, for malleable cast iron valves – from -30 to +120˚С, for brass and bronze valves – from -30 to +120 ˚С, for titanium alloys – from -40 to + 50 ˚С. At increase of operating medium temperature the tolerable operating pressure should be decreased depending on the material of the valves body details. Valves are produced from carbon steel for operating temperatures up to 445 ˚С, from grey cast iron – up to 300˚С, from malleable cast iron – up to 400˚С, from bronze and brass – up to 250 ˚С, from titanium – up to 350 ˚С.
Examples of designation codes under ГОСТ 356-80:
- Nominal pressure of 40 kgf/sq.cm. - Ру 40 or PN 40
- Test pressure of 60 kgf/sq.cm. – Рпр 60
- Operating pressure of 250 kgf/sq.cm. under the temperature of 530 ˚С – Рр 250 t 530
Table 7
Values of nominal pressures under ГОСТ 26349-84
MPa
| kgf/sq.cm.
| MPa
| kgf/sq.cm.
| 0,01
| 0,1
| 6,3
| 63
| 0,016
| 0,16
| 8,0
| 80
| 0,025
| 0,25
| 10,0
| 100
| 0,040
| 0,4
| 12,5
| 125
| 0,063
| 0,63
| 16,0
| 160
| 0,1
| 1
| 20,0
| 200
| 0,16
| 1,6
| 25,0
| 250
| 0,25
| 2,5
| 32,0
| 320
| 0,4
| 4
| 40,0
| 400
| 0,63
| 6,3
| 50,0
| 500
| 1,0
| 10
| 63,0
| 630
| 1,6
| 16
| 80,0
| 800
| 2,5
| 25
| 100,0
| 1000
| 4,0
| 40
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