Steam Control Valves - Calculate Flow Factor Kv

Calculator for determining the flow factor (Kv) for steam control valves using the formula: Kv = m / (31.7 * √(dP / v)). Based on pressure coefficient tables and steam flow specifications.

Calculator

Inputs

Steam Flow (m) (kg/h)

Pressure Drop (dP) (bar)

Specific Volume of Steam (v) (m³/kg)

Results

Flow Factor (Kv)--

Step 1: Determine Pressure Coefficient (Pcoef)

The pressure coefficient is determined from steam tables based on:

Absolute inlet pressure (bar)
Pressure drop across the valve (bar)

Important: Pressure drop cannot exceed approximately 42% of inlet pressure (critical pressure drop).

Formula: Pcoef = pressure drop / specific volume

Example

For 10 bar absolute pressure with 3.5 bar pressure drop:

Pcoef = 18.4 (from steam tables)

Step 2: Determine Flow Factor (Kv)

Find the pressure coefficient (Pcoef) column closest to your calculated value
Follow the column down to find your steam flow rate
Interpolate between values if necessary
Read the corresponding Kv value from the left column

Example

For Pcoef = 18.2 and steam flow = 592 kg/h:

Flow Factor Kv = 4.4

Kv	1	1.25	1.56	1.95	2.44	3.05	3.81	4.77	5.96	7.45
0.01	0	0	0	0	1	1	1	1	1	1
0.02	0	1	1	1	1	1	1	1	1	1
0.02	1	1	1	1	1	1	2	2	2	2
0.03	1	1	1	2	2	2	2	3	3	3
0.05	2	2	2	2	3	3	3	4	4	4
0.08	2	3	3	3	4	4	5	5	6	7
0.11	4	4	5	5	6	6	7	8	9	10
0.17	5	6	7	8	8	9	11	12	13	15
0.26	8	9	10	11	13	14	16	18	20	22
0.38	12	14	15	17	19	21	24	27	30	33
0.58	18	20	23	26	29	32	36	40	45	50
0.86	27	31	34	38	43	48	54	60	67	75
1.3	41	46	51	57	64	72	80	90	100	112
2.0	62	69	77	86	96	108	120	135	151	168
2.9	93	103	116	129	145	162	181	202	226	253
4.4	139	155	174	194	217	242	271	303	339	379
6.6	208	233	260	291	325	364	407	455	508	568
9.9	312	349	390	436	488	546	610	682	763	853
14.8	468	524	586	655	732	818	915	1023	1144	1279
22.2	703	786	878	982	1098	1228	1373	1535	1716	1918
33.3	1054	1179	1318	1473	1647	1841	2059	2302	2574	2877
49.9	1581	1768	1976	2210	2471	2762	3088	3453	3860	4316
74.8	2372	2652	2965	3315	3706	4143	4632	5179	5790	6474
112	3558	3978	4447	4972	5559	6215	6948	7769	8686	9711
168	5336	5966	6671	7458	8338	9322	10423	11653	13028	14566
253	8005	8949	10006	11187	12507	13983	15634	17479	19543	21849
379	12007	13424	15009	16780	18761	20975	23451	26219	29314	32774
568	18010	20136	22513	25170	28141	31463	35177	39329	43971	49161
852	27016	30204	33769	37755	42212	47194	52765	58993	65956	73741
1278	40523	45307	50654	56633	63318	70791	79147	88489	98934	110612