How do I select a control valve?

Select a control valve in nine stages: collect process data, calculate the required Cv or Kv, check for choked flow, flashing and cavitation, choose the valve body type, choose the flow characteristic, specify pressure class and materials, select the actuator and fail position, verify performance, then complete the specification sheet. Bore size follows from the calculated Cv, not from the pipe size.

How is Cv calculated for a control valve?

Cv is the US liquid flow coefficient: the flow in US gallons per minute that produces a 1 psi pressure drop across the valve at fully open with water at about 60 degrees Fahrenheit. For liquids, Cv = 1.96 x Ft x Q divided by N x Fl x Fp x the square root of (P1 minus P2), where Q is flow in gpm, N is the number of flow paths, P1 and P2 are upstream and downstream pressure in psia, and Ft, Fl and Fp are temperature, liquid recovery and piping geometry correction factors.

What is the difference between Cv and Kv?

Cv and Kv measure the same flow capability in different units. Cv uses US gallons per minute at a 1 psi drop, Kv uses cubic metres per hour at a 1 bar drop. Kv is approximately equal to 0.865 times Cv, and Cv is approximately equal to 1.156 times Kv.

What is the difference between linear and equal percentage flow characteristics?

A linear trim has a constant slope, so 50 percent of rated travel gives roughly 50 percent of rated flow. An equal percentage trim has a constant proportional change, so 50 percent travel gives about 50 percent of rated Cv. Use linear trim when process gain is constant, and equal percentage trim when pressure drop or system resistance varies, which is the most common case.

What does ATO and ATC mean on a fail-safe actuator?

ATO means air to open, so loss of air supply closes the valve and the valve fails closed. ATC means air to close, so loss of air supply opens the valve and the valve fails open. Pneumatic spring-return actuators are ATO or ATC as standard. Electric actuators achieve fail position through a return spring, a stored-energy mechanism, or a battery or UPS backed drive.

Should a control valve be sized for maximum flow?

Not necessarily. A valve sized only for peak flow spends most of its life near 10 percent open, where the trim sees high velocity, noise, vibration and rapid wear. Target steady operation between about 20 and 80 percent of rated travel. If maximum flow is rare, consider a split-range arrangement, two valves in parallel, or an interchangeable trim.

How do I prevent cavitation in a control valve?

Cavitation occurs when vapour bubbles form and collapse in the throat. Control it by keeping downstream pressure above the fluid vapour pressure, reducing the pressure drop across a single stage, using multi-stage or staged trim, specifying an anti-cavitation cage, selecting a larger bore and trimming the flow so velocity stays low, and avoiding high recovery factors downstream of the valve.

What is valve rangeability?

Rangeability is the ratio of maximum to minimum controllable Cv. A conventional globe valve typically offers 30 to 50 to 1, while characterized trim can reach 100 to 1 or more. Practically, most process control loops need a turndown of only about 30 to 1 between the minimum controllable and maximum rated stroke.

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Face-to-face valve dimensions - EN-558-1

Standard Hits: 175

EN-558-1 : Industrial valves, Face-to-face and centre-to-face
Dimensions of metal valves for use in flanged pipe systems - PN and Class designated valves

The EN 558 norm compiles several intenational standards for face-face distances on valves.
The numbers of the existing ISO basic series are maintained as in ISO 5752:1982.

(Note: Valve manufacturers catalogues are the source of the following information. Valvias is not responsable of any due to wrong information. Use the original standards for more feseable data.)

Origin of the Basic Series

Serie 1: DIN 3202-1/F1	Serie 9: DIN 3202/F33	Serie 18: BS 5154
Serie 2: DIN 3202-1/F2	Serie 10:ANSI B16.10 BS 1803	Serie 19: ANSI B16.10
Serie 3: ANSI B16.10	Serie 11: ANSI B16.10	Serie 20: API 609 BS 5156
Serie 4: ANSI B16.10	Serie 12:ANSI B16 10 BS 5353	Serie 21: ANSI B16.10
Serie 5: ANSI B16.10	Serie 13: BS 5155	Serie 22: BS 2080
Serie 6:	Serie 14: DIN 3202/F4	Serie 23: BS 2080
Serie 7: BS 2080	Serie 15: DIN 3202/F5	Serie 24: ANSI B16.10
Serie 8: DIN 3202-1/F32	Serie 16: API 609 BS 3135	Serie 25: MSS SP 67 - BS2080
Serie 9: DIN 3202-1/F33	Serie 17: API 600

Units: mm

DN	Basic Series
DN	1	2	3	4	5	6	7	8	9	10	11	12
10	130	210	102	-	-		108	90	105	-	-	130
15	130	210	108	140	165		108	90	105	108	57	130
20	150	230	117	152	190		117	95	115	117	64	130
25	160	230	127	165	216		127	100	115	127	70	140
32	180	260	140	178	229		146	105	130	140	76	165
40	200	260	165	190	241		159	115	130	165	83	165
50	230	300	178	216	292		190	125	150	203	102	203
65	290	340	190	241	330		216	145	170	216	108	222
80	310	380	203	283	356		254	155	190	241	121	241
100	350	430	229	305	432		305	175	215	292	146	305
125	400	500	254	381	508		356	200	250	330	178	356
150	480	550	267	403	559		406	225	275	356	203	394
200	600	650	292	419	660		521	275	325	495	248	457
250	730	775	330	457	787		635	325		622	311	533
300	850	900	356	502	838		749	375		698	349	610
350	980	1025	381	762	889			425		787	394	686
400	1100	1150	406	838	991			475		914	457	762
450	1200	1275	432	914	1092			500		978	483	864
500	1250	1400	457	991	1194					978		914
(500)	1350	-	483	1092	1295					1067		1016
600	1450	1600	508	1143	1397					1295		1067
(600)	1550	-	559	1245	1446					1295
700	1650		610	-	-					1448
750	1750		610	1397	1651					1524
800	1850		660							1676
900	2050		711							1956
1000	2250		813
1200
1400
1600
1800
2000

Units: mm

DN	Basic Series
DN	13	14	15	16	17	18	19	20	21	22	23	24	25
10	-	115	-	-	-	80	-	-	-	65	70	-	-
15	-	115	-	-	140	80	140	-	152	65	70	83	-
20	-	120	-	-	152	90	152	-	178	70	75	95	-
25	-	125	120	-	165	100	165	-	216	80	85	108	-
32	-	130	140	-	178	110	178	-	229	90	95	114	-
40	106	140	240	33	190	120	190	33	241	5	100	121	-
50	108	150	250	43	216	135	216	43	267	105	115	146	-
65	112	170	270	46	241	165	241	46	292	115	125	165
80	114	180	280	64	283	185	283	46	318	125	135	176	49
100	127	190	300	64	305	229	305	52	356	135	146	216	56
125	140	200	325	70	381		381	56	400			254	64
150	140	210	350	76	403		403	56	444			279	70
200	152	230	400	89	502		419	60	533			330	71
250	165	250	450	114	568		457	68	622			394	76
300	178	270	500	114	648		502	78	711			419	83
350	190	290	550	127	572		572	78	838				92
400	216	310	600	140	838		610	102	864				102
450	222	330	650	152	914		660	114	978				114
500	229	350	700	152	991		711	127	1016				127
(500)	-	-	750	170	-		749	154	1118				-
600	267	390	800	178	1143		787	154	1346				154
(600)	-	-	850	210				165	1346
700	292	430	900	229				165	1499
750	-	-	950	230				190	1594
800	318	470	1000	241				190	1778
900	330	510	1100	241				203	2083
1000	410	550	1200	300				216
1200	470	630		350				254
1400	530	710		390				279
1600	600	790		440				318
1800	670	870		490				356
2000	760	950		540				406

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Face-to-face valve dimensions - EN-558-1

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