- 11 -
Protection From Debris
On new installations, care must be taken to protect the meter from damage during start-up. It is
recommended that a strainer be installed upstream of the meter. Damage may result from the
passage through the meter of dirt, sand, welding slag or spatter, thread cuttings, rust, etc.
It is recommended that a spool be constructed to be installed in place of the meter until the
system is flushed. The spool is a flanged length of pipe equal in length to the meter and its
attached accessories. The meter may be left in place if the plumbing can be temporarily
bypassed around the meter to protect the meter from debris. Once the system has run “clean” for
a period of time the meter may be reinstalled or temporary protective devices removed.
Thermal Expansion
Most liquids will expand and contract with temperature. In any system where there is a chance
for liquid to be captured between closed valves without relief, there is a risk of thermal
expansion. This condition can create dangerously high pressures within the system. For every
one degree of temperature increase, there is a corresponding pressure increase of 126 PSI (8.69
BAR).
Care must be taken in designing the system where thermal shock may occur by implementing
Pressure Relief Valves or Thermal Expansion Joints in the system design.
Hydraulic Shock (Water Hammer)
Hydraulic shock is a rise in pressure that occurs when an operating system has immediate change
in direction of flow. This can be due to a sudden valve closure while the system is operating at a
at a high flow rate. Hydraulic shock can damage any item in the way of the product flow such as
the internal parts of the meter, valves, and pump. System design and improper operating
procedures will increase the risk of this problem. The use of 2-stage preset control valves or
surge suppressing bladders or risers will help reduce or eliminate this problem.
The shock pressure when a valve is closed quickly is computed as follows. The maximum
recommended shock pressure is 6 PSI.
Shock Pressure (PSI) = 63 x Velocity (FPS)
In order to eliminate hydraulic shock from sudden valve closure, the valve closure rate must be
reduced. The time required to close the valve so that the line pressure will not exceed the normal
pressure at zero flow is calculated as follows.
Time (seconds) = 0.027 x L x V
N – F
V = Velocity in Feet/Seconds
L = Length of pipe before the valve in feet
N = Line pressure at no flow
F = Line pressure at full flow
