ppt on design of penstock

1. DESIGHN OF PENSTOCK PIPE
Submitted by-
Md Zafar Alam
13512017
(2013-15)
M.Tech 1st
Year

2. INTRODUCTION
 Pressure conduits carrying water from forebay tank to
the power house are termed as penstock. Penstocks are
required to bear maximum water pressure including water
hammer.
 They are quite costly and are a very important part of
the water conductor system. As such
they should be designed and installed at the site with
utmost care.

3. TYPES OF PENSTOCKS
 According to location – The penstocks may be buried
inside the ground or they can be installed on surface along
the natural terrain.
(i)Buried penstocks – Such penstocks are installed inside a
trench and continuously supported on the soil at the
bottom of the trench.
(ii) Exposed penstocks:- They are laid along the profile of the
existing terrain on the hill slope preferably on the ridge of
the hill.

4. COMPONENTS OF PENSTOCK
Anchor block
Drain valve
Air bleed valve
support piers

6. SIZING OF PENSTOCK PIPE
 Sizing of penstock pipe means to calculate the
diameter and thickness of penstock pipe by
taken head loss ad cost in consideration.
Calculation of penstock diameter-
constraints in determining diameter
i.Cost
ii.Head loss

7. Continued………
 A smaller size penstock saves cost of construction
material but the loss of energy due to loss of head takes
place and vice versa. Due to this fact, we need to deduce
optimum diameter which has minimum cost and minimum
loss of energy.
Economical Diameter of Penstock

10. MAJOR CONTRIBUTIONS TO HEAD LOSS
i. Friction (due to surface roughness)
h f = ½. V2.L.f / g.D
Darcy’s equation
V – flow velocity
L – penstock length
D –diameter
f -- friction constant
(from moody chart)
ii. Turbulence ( caused by due to bends ,inlet,
valves,leaving etc).

13. WALL THICKNESS CALCULATION
Constraints in deciding wall thickness-
i. Cost
ii. Strength (withstanding pressure)
 Wall should be thick enough to withstand the maximum
water pressure.
Maximum pressure = static + surge
hsurge = C .V / 2g
v= flow velocity
C=velocity of pressure wave
tinitial= (D+50)/400 in cm
Where D is in cm

16. AIR VENTS
These are provided on the immediate downstream side of
the control gate or valve to facilitate connection with the
atmosphere.
 Air inlets serve the purpose of admitting air into the pipes
when the control gate or valve is closed and thepenstock is
drained, thus avoiding collapse of the pipe due to vacuum
excessive negative pressure.
 Similarly,when the penstock is being filled up, these vents
allow proper escape of air from the pipes. The factors
governing the size of the vents are length,diameter,
thickness, head of water, and discharge in the penstock and
strength of the penstock under external pressure.

17.  Size of the air vent may be determined by the
following formula
Where-
F = area of air inlet in m2,
Q = flow of air thro-ugh inlet in m3/s,
S = factor of safety against collapse of pipe,
C = co-efficient of discharge through airvent
( generally 0.6 1,
d = diameter of steel pipe in mm, and
t = thickness of steel pipe in mm.

18. Thank you for your
attention…..

19. REFFERENCES
i. Ahec iit roorkee
ii. Design-of-Penstock Is code-11639,11625,9761
iii. scribd.com