8. Single bellows pressure gauge:
•A single bellows pressure gauge measures pressure relative to
atmospheric pressure, in other words, gauge and vacuum
pressure. System media flows into the pressure gauge through
the gauge’s pressure inlet.
• For low pressure applications, fluid flows directly into the
bellows and for high pressure applications, it flows around the
bellows.
•The difference in pressure inside and outside of the bellows
causes it to expand or contract. The bellows is mechanically
linked to the pointer.
•Bellows expansion and contraction proportionally moves the
pointer to indicate the pressure.
•Bellows are typically spring-loaded, preventing their full
expansion, which minimizes the potential for damage to the
bellows.
9. Dual bellows pressure gauge
•Dual bellows pressure gauges are typically used to measure
absolute pressure. One bellows is evacuated and sealed,
making it a perfect vacuum. The other bellows is connected to
the system process pressure.
•The two bellows are joined by a motion balance mechanism on
a fixed pivot. Increase in system pressure causes the
measuring bellow to expand, which tilts the motion balance
mechanism and moves the needle that indicates absolute
pressure.
•Dual bellows pressure gauges are also suitable for measuring differential
pressure. One bellows connects to the low pressure side of the system and
the other bellows connects to the high pressure side.
• Each bellows influences the movement of the pointer mechanism to show
the difference in pressure impacting the bellows.
12. •Diaphragm is preferably suitable for the gauge, absolute, and
differential pressure measurement.
•The diaphragm pressure gauge has a circular, corrugated
diaphragm as the main element which is clamped or welded
between a pair of the flange.
•Diaphragm is generally manufactured from resilient steels such
as stainless steel or Inconel.
•The deflection of the pressure element is transferred via a link or
mechanism. This mechanism amplifies the small deflection of the
element and transfers it to the pointer
15. Apparatus for Reynolds experiment are :
1. A tank containing water at constant head
2. A small tank containing some dye
3. A glass tube with bell-mouthed entrance at one end and a regulating valve
at other end
• Now we will allow water to pass through the glass tube We will introduce a
liquid dye, of having same specific weight as of water, in to the from the
water tank.
• Regulating valve is provided here to vary the velocity of water flowing
through the glass tube.
Observation I
• When velocity of water flow is low, dye filament will be in the form of
straight line in the glass tube. It could be seen in the glass tube that dye
filament is in the form of straight line and parallel to the wall of glass
tube. Above condition is the example of laminar fluid flow. Therefore at
lower velocity of water flow through the glass tube, the type of water flow
will be laminar.
16. Observation II
•Now velocity of flow is increased with the help of regulating valve. Dye
filament will not be in the form of straight line in the glass tube. It could be
seen in the glass tube that dye filament is in the form of wavy one now.
•Above condition is the example of transition of fluid flow. Transition flow
means the flow between laminar flow and turbulent flow.
Observation III
Now velocity of flow is increased again with the help of regulating valve. Wavy
dye filament will be broken and finally diffused in the water
It could be seen in the glass tube that particles of dye filament liquid are
moving in random and irregular fashion at this higher velocity of water flow.
Mixing of particles of water and dye filament is intense and water flow will be
random, irregular and disorderly.
Above condition is the example of turbulent fluid flow. Therefore when velocity
of water flow will be higher, the type of water flow will be turbulent flow.
