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.NoType of ValveCost Per Valve in UD $
1Bellow Seal valves75$
2Piston Vlave38$
3Standerd Globe Valve20$

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 ValveCost On SparesCost of labourDowntime
Bellow Seal valvesNillNillNone
Piston Vlave5$12$2 Hours
Globe Valve1.25$6$

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 ValveCost On SparesCost ofDowntime
Cost Of Loss Of Media/Energy
Bellow Seal valvesNillNillNone
Piston VlavePriceless`12$160$ per month
Globe ValvePriceless6$160$ 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 ValveIIIIIITotal
Bellow Seal valves75$NillNone75$
Piston Vlave38$17$5$/Day (US $ 160/30 Days)55$ + 5$ / Day
Standard Globe20$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