Question

A penstock is 2000 m long and the velocity of pressure wave in it is 1000 m/s. Water hammer pressure head for instantaneous closure of valve at the downstream end of pipe is 60 m. If the valve is closed in 4 sec, then the peak water hammer pressure head is equal to

• A. 15 m
• B. 30 m
• C. 60 m
• D. 120 m

Answer 1

The correct option is C 60 m

We know that critical time is given by

$T_0=\frac{2L}{C}$

$\Rightarrow T_0=\frac{2\times 2000}{1000}$

$\Rightarrow T_0=4s.$

Actual time for valve closure, T =4 s.

$\text{Actual time for valve closure,}T=4s.$

$\text{We know that if}T\le T_0,\text{then the closure is known as rapid closure or instantaneous closures.}$

Therefore the peak water hammer pressure will be equal to the water hammer pressure head for instantaneous closure of the valve at the downstream end i.e. 60 m.