Press reguladores de presion

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Pre s sure -Re ducing Re gulator Flow Cur ve s
Te chnic al Bulletin
Scope
Selecting a regulator for an application first requires review of its performance capabilities and their alignment with the application’s requirements. The best starting point is the regulator’s flow curve provided by the manufacturer, because it illustrates the regulator’s range of capabilities atone glance. The curve represents the range of pressures that a regulator will maintain given certain flow rates in a system. This technical bulletin provides an overview of how to read regulator flow curves for pressure-reducing regulators. It describes some of the complexities, including droop, seatload drop or lockup, choked flow, hysteresis, and supply pressure effect (SPE), also known asdependency. In addition, SPE values and flow curves for KPR series pressure-reducing regulators are provided for the full line of maximum inlet pressure ranges and flow coefficients available. Swagelok®
Pressure Control Ranges
0 to 250 psig (0 to 17.2 bar)
0 400 400 800 1200

0 to 500 psig (0 to 34.4 bar)
1600 25 20

Nitrogen Flow, std L/min

Outlet Pressure, psig

300

500 psig (34.4 bar)200

1000 psig (68.9 bar)

Outlet Pressure, bar

Inlet Pressure 2200 psig (151 bar)

15 10

USA

100

500 psig (34.4 bar)

1000 psig (68.9 bar)
20 30 40

2200 psig (151 bar)
50 60 70

5.0 0

0

10

Nitrogen Flow, std ft3/min Fig. 1. Manufacturers often provide multiple flow curves for the same regulator at different inlet pressures to provide a range of the 10 20 30 4050 60 70 0 regulator’s operating capabilities.
400 25

The Basics
A regulator’s main purpose is to maintain a constant pressure on one side of the regulator even though there is a different pressure or fluctuating pressure on the other side. In the case of a pressure-reducing regulator, pressure is controlled downstream of the regulator. A flow curve illustrates a regulator’s performance interms of outlet pressure (Y axis) and flow rate (X axis). Flow is not controlled by the regulator. It is controlled downstream by a valve or flow meter. The curve shows how a regulator will respond as flow in the system changes. Let us examine how to read a flow curve. Examine the top curve in Fig. 1. The curve starts at 400 psig (27.5 bar), but drops slightly as flow increases across most of thegraph.

When reading a flow curve, identify the range of flows 300 that 20 are seen in the system. Then, mark them on the graph to see what the corresponding changes in outlet pressure will 15 200 be. Is that range of pressures acceptable? If not, a different 10 regulator is needed. Ideally, a regulator operates best on the flattest part of100 the 5,0 curve, and will maintain relatively constantpressures, even with significant changes in flow. At the extreme ends of 0 0 400 1200 1600 the curve, however, there800 steep drops where pressures are change dramatically with even the slightest change in flow. The regulator will not operate at the highest level of efficiency at these locations. For every set pressure, there is a different curve. In Fig. 1, there2.5 two main sets of curves: onebased on a set are pressure of 400 psig (27.5 bar) and one on a set pressure of 2.0 200 psig (13.7 bar). If the desired set pressure lies between the curves, one can interpolate. Note that the two curves 1.5 are close to the same shape but in different locations on the graph. 1.0 There is one additional variable that affects the shape of a 0.5 curve—the inlet pressure (i.e., pressure going into apressurereducing regulator on the upstream side). Note that for each of the 0 two sets of curves 800 Fig. 1,1200 are three curves in there 1600 400 representing a range of inlet pressures.

EUR

JAPA

0 25 20 15 10

10

20

30

40

50

60

70 2.5 2.0 1.5 1.0

CHIN

2

Pressure-Reducing Regulator Flow Curves
Nitrogen Flow, std L/min
0 80 70 500 1000 1500 2000 2500 3000...
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