Butterfly Valve Torque Standards And Testing Methods

In industrial production and daily life, butterfly valves play a crucial role as key devices for controlling fluid flow. The torque of a butterfly valve is an important performance indicator, directly impacting ease of operation, reliability, and lifespan. A deeper understanding of butterfly valve torque is essential for improving operational efficiency.

What is Butterfly Valve Torque?

Butterfly valve torque refers to the torque required to open or close the valve. It is generated by the combined effects of friction between internal components such as the seals, stem, and valve body, as well as fluid pressure. The magnitude of butterfly valve torque depends on several factors, including valve size, operating pressure, fluid medium, and temperature. It is typically measured in Newton-meters (N·m).

Importance of Butterfly Valve Torque

The torque setting of a butterfly valve directly impacts its smooth operation, sealing quality, and durability. Proper torque reduces wear, prevents leaks, protects actuators, and aids in energy efficiency. A well-set torque ensures stable and reliable valve performance.

Five Factors Influencing Torque in Concentric Butterfly Valves

1. Seat Torque
   Friction force when the valve disc disengages from the elastic seat.

2. Bearing Torque
   Friction between the bushing surface and the shaft.

3. Dynamic Torque
   Force exerted on the valve disc by the fluid flowing through the valve. Dynamic torque is generally not a primary concern for elastomer-seated butterfly valves unless the flow rate exceeds 6 m/s, in which case dynamic torque should be considered when selecting an actuator.

4. Valve Size and Pressure Rating
   The larger the valve size, the greater the torque required. Similarly, higher pressure ratings increase the torque.

5. Fluid Properties
   Characteristics of the fluid, such as viscosity, density, and temperature, impact the butterfly valve's torque.

Methods for Measuring Butterfly Valve Torque

1. Using a Torque Wrench

   Operate the valve manually with a torque wrench and record the required torque value. This method is suitable for manual valves but requires consistent measurements.

2. Electronic Torque Sensor

   Install an electronic torque sensor on the valve's operating shaft to record real-time torque values during opening and closing. This method is highly accurate and suitable for large or automated valves.

3. Hydraulic Testing Equipment

   For hydraulically operated valves, hydraulic testing equipment can measure torque by controlling system pressure, providing torque values at different operational states.

4. Actuator-Built-in Torque Measurement

   Some electric or pneumatic actuators have built-in torque measurement capabilities, automatically recording torque data during valve operation. This method is ideal for automated systems, offering real-time and precise data.

5. Calculation Method

   The calculation method determines the opening torque by theoretically calculating based on valve structure parameters, fluid properties, and operating conditions.

Note:

When calculating valve torque, it’s essential to consider friction between the valve disc and seat, friction between the stem and packing, and the thrust exerted on the disc by different pressure differentials. Due to the wide variety of materials for the disc, seat, and packing—each with unique friction coefficients, contact areas, and compression levels—calculated torque values serve as a reference but are affected by numerous factors. Therefore, actual measurement is generally preferred over theoretical calculation.

Total torque can be calculated as follows:

Ta = Ts + Tb + Td

Where:    

Ta : The required actuator torque

Ts=Seat Torque

Tb=Bearing Torque

Td=Dynamic Torque

Tb = Qc * fC * Ds / 2  

Where:  

P=Normal Pressure

Fc=Fricton Coefficient

Ds=Shaf Diameter

Td = Ct * D3 *△ P

Where:

Td=Dynamic Torque Coefficient

D=Valve Normal Diameter

△ P=Pressure Drop

Ts = Qm * R / 1000

Where:

Qm=Fricton of Sealing Face

Qc=Bearing Loading

R =Radius Disc

Example Table of Butterfly Valve Torque

Torque specifications are based on optimum test conditions. Actual torques may vary under different field and environmental applications.

The torque figures provided represent the required torque to open and re-seat the valve. The figures provided are based upon water and other lubricating fluids, and include a factor of safety.

Table 1:Rubber Seat Butterfly valve torque chart example

Valve size		Torque Value for Rubber Seat Butterfly Valve (N.m)
		PN6 (85PSI)		PN10(16PSI)		PN16 (250PSI)
inch	mm	dry	wet	dry	wet	dry	wet
1.5”	40	11.5	8	18.5	9	22	11
2”	50	20.3	12.5	22.1	13.9	24.2	15.1
2.5”	65	26.1	13.8	29.2	15.4	32.7	17.2
3”	80	39.9	21	41.1	21.7	43.7	23.1
4”	100	60.5	34.9	67.8	37.1	72.8	39.8
5”	125	85.1	53.5	101	57.9	108	61.9
6”	150	149	84.5	165	93.9	174	102
8”	200	264	154	297	173	330	192
10”	250	423	249	486	286	549	323
12”	300	605	371	699	429	799	490
14”	350	699	466	825	550	970	625
16”	400	948	632	1133	755	1307	846
18”	450	1247	831	1253	1012	1788	1131
20”	500	1639	1093	1617	1350	2308	1431
24”	600	2519	1679	2622	2111	3711	2301
28”	700	4511	3008	4903	3269	6850	5670
30”	750	5222	3482	5677	3785	7916	6782
32”	800	5939	3762	6456	4304	9180	7840
36”	900	7363	4949	7879	5252	13786	10150
40”	1000	12539	8359	13377	8917
42”	1050	14300	9538	15291	10193
44”	1100	16301	10867	17390	11592
48”	1200	17585	11723	18816	12735

Table 2:Teflon Seat Butterfly valve torque chart example

Valve size		Torque Value for Teflon Seat Butterfly Valve (N.m)
		PN6 (85PSI)		PN16 (250PSI)
inch	mm	dry	wet	dry	wet
1.5”	40	31.3	19.4	36.2	23
2”	50	39.1	24.3	45.2	28.2
2.5”	65	48.8	35	61	32.1
3”	80	74.6	39.4	81.8	43
4”	100	119.3	65.3	136	74.3
5”	125	175	100.6	202	116
6”	150	278	158	325	191
8”	200	494	287	617	358
10”	250	790	465	1026	603
12”	300	1132	694	1493	916
14”	350	1814	1153	1905	1269
16”	400	2398	1394	2518	1534
18”	450	3340	2047	3508	2252
20”	500	4122	2449	4329	2694
24”	600	7044	3882	7396	4270

Butterfly Valve Kv Value

The Kv value (flow coefficient) of a butterfly valve is an indicator used to measure the flow capacity of the valve. The Kv value represents the water flow rate through the valve when fully open, under specified conditions. Specifically, it is defined as the volume of water (in cubic meters per hour, m³/h) that flows through the valve with a pressure differential of 1 bar across the valve ends.

CV=1.17KV

KV
Diameter/DN		Disc Position (Angle of Opening)
mm	inch	10°	20°	30°	40°	50°	60°	70°	80°	90°
40	1-1/2	0	1	3	6	11	18	30	53	59
50	2	0	2	5	12	21	35	59	105	117
65	2 1/2	0	4	11	25	46	76	126	226	251
80	3	1	7	21	46	82	137	228	410	455
100	4	1	10	31	70	124	207	345	621	690
125	5	2	23	68	152	273	455	759	1366	1518
150	6	3	35	108	242	435	725	1209	21776	2418
200	8	5	73	220	586	897	1479	2465	4426	4929
250	10	9	136	410	921	1675	2792	4653	8375	9306
300	12	10	150	455	1023	1861	3102	5170	9306	10340
350	14	12	179	543	1218	2217	3734	6223	11201	12445
400	16	14	204	441	1386	2521	4247	7078	12740	14155
450	18	18	276	836	1879	3418	5757	9595	17271	19190
500	20	23	360	1093	2455	4467	7524	12672	22810	25344
600	24	31	466	1412	3171	5770	9719	16368	29462	32736
700	28	37	564	1710	3841	6988	11771	19824	35683	39648
800	32	42	642	1950	4380	7969	13424	22608	41118	45687
900	36	54	814	2467	5543	10084	16986	28608	52031	57812
1000	40	75	1127	3420	7682	13976	23541	39648	72110	80948
1200	48	101	1529	4637	10416	18950	31920	53760	97776	109760

Manufacturer reserves the right to modify dimensions, materials, or design. Consult factory for certification.If you have any other questions, please feel free to contact TFW Valve