Economics Of Using A Bellow Seal Valve
For analyzing the cost benefits of a Bellow Seal Valve over a Piston Valve or a conventional Gate / Globe Valve we will consider a 15mm valve operating on STEAM at 150 psi, in three types of valve.
1. Bellow Seal Valve
2. Piston Valve
3. Standard Globe Valve
A) Capital Cost: We can estimate the cost per unit as follows
| S.No | Type of Valve | Cost Per Valve in UD $ |
| 1 | Bellow Seal valves | 75$ |
| 2 | Piston Vlave | 38$ |
| 3 | Standerd Globe Valve | 20$ |
B) Maintainance cost: Assuming that gland leakage will begin within a period of 6 months in a Standard Globe Valve and in a period of 9 months in a Piston Valve, then maintainance costs will be as follows:
| Type of Valve | Cost On Spares | Cost of labour | Downtime |
| Bellow Seal valves | Nill | Nill | None |
| Piston Vlave | 5$ | 12$ | 2 Hours |
| Globe Valve | 1.25$ | 6$ | 1 Hour |
Assuming cost of spare piston rings at US$ 5 per pair of rings.
Assuming a down time of 2 hours x labour cost of US$ 6 per hour of maintainance.
Assuming cost of gland packing at US$ 1.25
Assuming a downtime of 1 hour x labour cost of US$ 6 per hour of maintenance.
B) Cost of Downtime & Energy/Media Loss:
We will assume a gland clearance of 1 thou (0.001 inches) for estimation of gland leakage and a cost of US$ 20 per tonne of steam. Steam will escape at a rate of 25 lbs/hr through this clearance (as per steam tables)
| Type of Valve | Cost On Spares | Cost ofDowntime | Cost Of Loss Of Media/Energy |
| Bellow Seal valves | Nill | Nill | None |
| Piston Vlave | Priceless | `12$ | 160$ per month |
| Globe Valve | Priceless | 6$ | 160$ per month |
If we assume leakage of 11 kgs/hrs/day=264 kgs (11 kgs x 24 hrs) of steam loss per day x 30 days = 7920 kgs x steam cost of US$ 20/Ton = US$ 160 per month of energy Loss which can be saved ! (USD 5 per Day Approx.) The cost of down time is priceless and a value as such can not be put on it. It can vary from a few hundred to millions of US$ per day.
D) Total Cost of Ownership (TCO)= 1 + II + III
| Type of Valve | I | II | III | Total |
| Bellow Seal valves | 75$ | Nill | None | 75$ |
| Piston Vlave | 38$ | 17$ | 5$/Day (US $ 160/30 Days) | 55$ + 5$ / Day |
| Standard Globe | 20$ | 7.25$ | 5$/Day (US $ 160/30 Days) | 27.25$ + 5$ / Day |
So lets estimate that if the leakage is not attended (which is not in most of the plants), the cost of the valve would
be as follows:
- Total cost of ownership for a Bellow Sealed Valve in 1 year would be: US$ 75.
- Total cost of ownership for a Piston Valve in 1 year would be: US$ 55+US$ 5/day x 90 days = US$ 505
(since we have assumed leakage will begin in 9 months) - Total cost of ownership for a Standard Globe Valve in year would be US$ 27.25 +(US$ 5/day x 180days
(since we have assumed leakage will begin in 6 months) = US$927.25
