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 shall 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
|Sr. No.||Types of Valves||Cost per Valve in US$||I|
|1||Bellow Seal Valve||US$ 75|
|2||Piston Valve||US$ 38|
|3||Standard Globe Valve||US$ 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 of Spares||Cost of Labour||Downtime||II|
|Piston Valve||US$ 5||US$ 13||2 Hours|
|Globe Valve||US$ 1.25||US$ 6||1 Hour|
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 maintainance
C) 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 tonne of steam. Steam will escape at a rate of 25 lbs/hr through this clearance (as per steam tables).
|Type of Valve||Cost of Spares||Cost of Loss of Media / Energy||III|
|Piston||Priceless||US$ 120 per annum|
|Standard Globe||Priceless||US$ 120 per month|
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)= I + II + III
|Types of Valves||I||II||III||Total|
|Bellow Seal Valve||US$ 75||Nil||Nil||US$ 75|
|Piston Valve||US$ 38||US$ 18||US$ 4/Day (US$ 120/30 Days)||US$ 55 + US$ 4/Day|
|Standard Globe Valve||US$ 20||US$ 8||US$ 4/Day (US$ 120/30 Days)||US$ 26 + US$ 4/Day|
- 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$ 75+US$ 4/day x 90 days (since we have assumed leakage will begin in 9 months)
- Total cost of ownership for a Standard Globe Valve in year would be US$ 28 = US$ 435 =US$ 4/day x 180 days (since we have assumed leakage will begin in 6 months) = US$ 748