Question of the Month: 2015

Question of the Month for December 2015

QUESTION:

A slow opening valve requires____ complete turns to be fully open or closed?

A. Three

B. five

C.  Seven

D. Nine

ANSWER:

B: five

Question of the Month for November 2015

QUESTION:

Pigtail

Identify the parts of the pigtail siphon shown:

___ Gate Valve

___ To Pressure Gauge

___ To Inspector’s Test Gauge

___ To Boiler

ANSWER:

_B__ Gate Valve

_A__ To Pressure Gauge

_D__ To Inspector’s Test Gauge

_C__ To Boiler

Question of the Month for September 2015

QUESTION:

Soot Blower

Identify the parts of the soot blower.

           ___ Endless Chain

___ Packing

___ Element

    ___ Gooseneck

ANSWER:

Identify the parts of the soot blower.

           __C_ Endless Chain

__D_ Packing

__A_ Element

    __B_ Gooseneck

Question of the Month for August 2015

QUESTION:

A 3/4″ blowdown line may be used if the boiler has ___sq’ of heating surface.

a) more than 100

b) less than 199

c)  More than 500

d)  None of the above

ANSWER:

d)  None of the above

The minimum size drain required on a water column is 3/4 inch

Question of the Month for June 2015

QUESTION:

According to the ASME, when no boiler water analysis is made the boiler should be blown down at least once?

      a) 8 hours

        b) 24 hours

   c) month

d) week

ANSWER:

Weekly

The American Society of Mechanical Engineers (ASME) has developed a best operating practices manual for boiler blowdown. The recommended practices are described in Sections VI and VII of the ASME Boiler and Pressure Vessel Code. You can identify energy-saving opportunities by comparing your blowdown and makeup water treatment practices with the ASME practices. The ASME Boiler and Pressure Vessel Code can be ordered through the ASME Web site at http://www.asme.org/bpvc/.

Question of the Month for March 2015

QUESTION:

What organizations publish requirements for the various components which make up a fuel train for specific burner output?

ANSWER:

There are several organizations such as UL (Underwriters Laboratory), FM (Factory Mutual), IRI (Industrial Risk Insurers), etc, .

Question of the Month for February 2015

QUESTION:

Safety valve chatter in liquid service is potentially more serious than in vapor service. (T/F)

ANSWER:

True

Because of the liquid hammer effect.

Surge or water hammer, as it is commonly known is the result of a sudden change in liquid velocity. Water hammer usually occurs when a transfer system is quickly started, stopped or is forced to make a rapid change in direction. Any of these events can lead to catastrophic system component failure.Without question, the primary cause of water hammer in process applications is the quick closing valve, whether manual or automatic. A valve closing in 1.5 sec. or less depending upon valve size and system conditions, causes an abrupt stoppage of flow. The pressure spike(acoustic wave)created at rapid valve closure can be high as five (5) times the system working pressure.

Unrestricted, this pressure spike or wave will rapidly accelerate to the speed of sound in liquid, which can exceed 4000 ft/sec. It is possible to estimate the pressure increase by the following formula.

Water Hammer Formula: P = (0.070) (V) (L) / t + P1

Where  P = Increase in pressure

P1 = Inlet Pressure

V = Flow velocity in ft/sec

t = Time in sec.(Valve closing time)

L = Upstream Pipe Length in feet

Question of the Month for January 2015

QUESTION:

What type is the most widely used feedwater pump today?

ANSWER:

The centrifugal pump!

centrifugal pump

Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.  Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor.

A centrifugal pump converts input power to kinetic energy by accelerating liquid in a revolving device – an impeller.

The most common is the volute pump – where fluid enters the pump through the eye of the impeller which rotates at high speed. The fluid accelerates radially outward from the pump chasing and a vacuum is created at the impellers eye that continuously draws more fluid into the pump.

pump power si imperial units

The energy from the pumps prime mover is transfered to kinetic energy according the Bernoulli Equation. The energy transferred to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller is, the higher will the velocity of the liquid energy transferred to the liquid be. This is described by the Affinity Laws.

Pressure and Head

If the discharge of a centrifugal pump is pointed straight up into the air the fluid will pumped to a certain height – or head – called the shut off head. This maximum head is mainly determined by the outside diameter of the pump’s impeller and the speed of the rotating shaft. The head will change as the capacity of the pump is altered.

The kinetic energy of a liquid coming out of an impeller is obstructed by creating a resistance in the flow. The first resistance is created by the pump casing which catches the liquid and slows it down. When the liquid slows down the kinetic energy is converted to pressure energy.

  • it is the resistance to the pump’s flow that is read on a pressure gauge attached to the discharge line

A pump does not create pressure, it only creates flow. The gauge pressure is a measurement of the resistance to flow.

In fluids the term head is used to measure the kinetic energy which a pump creates. Head is a measurement of the height of the liquid column the pump could create from the kinetic energy the pump gives to the liquid.

  • the main reason for using head instead of pressure to measure a centrifugal pump’s energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not

The pump’s performance on any Newtonian fluid can always be described by using the term head.

Different Types of Pump Head

  • Total Static Head – Total head when the pump is not running
  • Total Dynamic Head (Total System Head) – Total head when the pump is running
  • Static Suction Head – Head on the suction side, with pump off, if the head is higher than the pump impeller
  • Static Suction Lift – Head on the suction side, with pump off, if the head is lower than the pump impeller
  • Static Discharge Head – Head on discharge side of pump with the pump off
  • Dynamic Suction Head/Lift – Head on suction side of pump with pump on
  • Dynamic Discharge Head – Head on discharge side of pump with pump on

The head is measured in either feet or meters and can be converted to common units for pressure as psi or bar.

  • it is important to understand that the pump will pump all fluids to the same height if the shaft is turning at the same rpm

The only difference between the fluids is the amount of power it takes to get the shaft to the proper rpm. The higher the specific gravity of the fluid the more power is required.

Note that the latter is not a constant pressure machine, since pressure is a function of head and density. The head is constant, even if the density (and therefore pressure) changes.

The head of a pump in metric units can be expressed in metric units as:

h = (p2 – p1)/(ρ g) + v22/(2 g) (1)

where

h = total head developed (m)

p2 = pressure at outlet (N/m2)

p1 = pressure at inlet (N/m2)

ρ = density (kg/m3)

g = acceleration of gravity (9.81) m/s2

v2 = velocity at the outlet (m/s)

Head described in simple terms

  • a pump’s vertical discharge “pressure-head” is the vertical lift in height – usually measured in feet or m of water – at which a pump can no longer exert enough pressure to move water. At this point, the pump may be said to have reached its “shut-off” head pressure. In the flow curve chart for a pump the “shut-off head” is the point on the graph where the flow rate is zero

Pump Efficiency

Pump efficiency, η (%) is a measure of the efficiency with wich the pump transfers useful work to the fluid.

η = Pout / Pin (2)

where

η = efficiency (%)

Pin = power input

Pout = power output