1. Selection of the Hydraulic Steel Pipe Flow Diameter Hydraulic steel tubing is a slender pipeline carrying oil; an excessively small bore diameter can result in high flow velocities, leading to significant pressure drops and heat generation. Conversely, an overly large bore diameter increases system costs. Therefore, selecting the optimal pipe size is critical.
Selection of the System Runner Diameter The pipeline flow diameter can be selected based on the required flow rate and pipe type, as shown in the table below. The table is based on the following recommended flow velocities: Working pipeline (pressure ≥ 10 bar): 8 m/s Return oil line (1 bar ≤ pressure ≤ 3 bar): 4 m/s Oil suction line (vacuum negative pressure): 1.2 m/s
Hydraulic oil
Maximum flow rate
L/min
Runner diameter [mm]
Pressure ≥ 10 bar
Working pipeline
Pressure: 1–3 bar
Oil return line
Vacuum negative pressure
Oil suction line
1
1.6
2.3
4.2
2
2.3
3.3
5.0
3
2.8
3.0
7.3
4
3.3
4.6
8.4
5
3.6
5.2
9.4
6
3.0
5.6
10.3
7
4.3
6.1
11.1
8
4.6
6.5
11.9
9
4.9
6.9
12.6
10
5.2
7.3
13.3
12
5.6
8.0
14.6
14
6.1
8.6
15.7
16
6.5
9.2
16.8
18
6.9
9.8
17.9
20
7.3
10.3
18.8
22
7.6
10.8
19.7
24
8.0
11.3
20.6
26
8.3
11.8
21.5
28
8.6
12.2
22.3
30
8.9
12.6
23.1
32
9.2
13.0
23.8
34
9.5
13.4
24.5
36
9.8
13.8
25.3
38
10.1
14.2
25.9
40
10.3
14.6
26.6
45
10.9
15.5
28.2
50
11.5
16.3
29.8
55
12.1
17.1
31.2
60
12.6
17.9
32.6
65
13.1
18.6
33.9
70
13.6
19.3
35.2
75
14.1
19.0
36.4
80
14.6
20.6
37.6
85
15.0
21.3
38.8
90
15.5
21.9
39.9
95
15.9
22.5
41.0
100
16.3
23.1
42.1
110
17.1
24.2
44.1
120
17.9
25.3
46.1
130
18.6
26.3
47.0
140
19.3
27.3
49.8
150
20.0
28.2
51.5
160
20.6
29.2
53.2
170
21.3
30.1
54.9
180
21.9
30.9
56.5
190
22.5
31.8
58.0
200
23.1
32.6
59.5
220
24.2
34.2
62.4
240
25.3
35.7
65.2
260
26.3
37.2
67.9
280
27.3
38.6
70.4
300
28.2
39.9
72.9
320
29.2
41.2
75.3
340
30.1
42.5
77.6
360
30.9
43.7
79.8
380
31.8
44.9
82.0
400
32.6
46.1
84.2
450
34.6
48.9
89.3
500
36.4
51.5
94.1
2> Flow calculation for throttling valves, with liquid as the working medium. The throttling orifice (a thin-walled small hole) in the valve passage determines the valve’s flow rate. The flow‑rate equation is applicable when both the upstream diameter and the downstream diameter, D, are at least 2.5 times the orifice diameter, d (D/d ≥ 2.5), and the ratio of the orifice length to its diameter, L/d, does not exceed 0.5.
Q (L/min): Liquid flow rate ΔP (MPa): Pressure difference C: Pressure loss coefficient, typically taken as 0.62 A (mm²): Area of the small circular hole with diameter d ρ (kg/m³): Liquid density (ρ_water = 998 kg/m³)
3> Relationship between valve flow rate Q and valve disc opening height H h: Valve disc opening height H: Effective Opening Height d: runner diameter/throat diameter A1: Flow passage area (diameter d) A2: Valve area (the annular window area between the valve disc and the valve seat)
Flow‑rate versus valve‑disc‑opening‑height curve (plane seal)
1. When h/d ≤ 1/20, the erosive force of the fluid is strong, The valve disc and valve seat must be made of metal. 2. When h/d = 1/4, A2 = A1. 3. When h/d ≤ 1/3, the flow rate Q is approximately proportional to h. 4. When h/d > 1/2, the flow rate Q is virtually independent of h.
