As valve is opened backpressure lowers and flow increases.

As valve is closed backpressure increases and flow lowers.

Body-main element of the valve;directs flow through the valve, past the disk and its mating surface (the seat)

Rising stem valves can be used to determine valve position.

Non-rising stem valves cannot.

remove system pressure from the packing in the event packing leakageis excessive and adjustment cannot correct the problem.

Describe the function and design characteristics, including advantages or disadvantages for gate valves.

Approx 80% of total flow through valve occurs in first 25% of stem movement

Advantages - good isolation valve: low head loss (d/p): can be fitted with any type of actuator.

Disadvantages - poor throttle valve: can't easily open against high d/p

Used to start, stop, and regulate flow.

Higher head loss (d/p) than gate valve.

Very good for throttling.

used to make fine adjustments to the amount of flow through the valve.

Long narrow point on end of valve allowing for more precise throttling than globe valve.

Not normally used as isolation valves due to delicate nature of valve.

Used to start, stop, and regulate flow in high flow, low pressure application.

When in full open position little to no resistance to flow - low d/p

Full closed - little to no seat leakage as long as seat is in good condition.

Throttle capabilities not as good as globe valve.

Used to stop and start flow.

Little resistance to flow when full open (low d/p)

Disadvantages - Cost, relatively rapid wear, inability to regulate flow.

Used to start, stop, and regulate flow.

Long lasting and reliable, no stem leakage, provides precision throttling, minimum pressure loss(d/p)

not used in high pressure or high temp systems

used primarily in radioactive and/or corrosive systems

Permit flow in only one direction.

Prevent backflow by closing when downstream pressure is greater than upstream pressure.

Types - Stop, Swing, Lift

Swing- offers little resistance to flow

Lift - resemble globe valve: more pressure loss

Stop - Capable of being closed by valve actuator: can stop flow in both directions.

Provide overpressure protection

Begins to open when system reaches valves setpoint

continues to open as pressure increases

valve will reclose when system pressure lowers below the pressure setpoint

Provides large volume release at low overpressure conditions.

Fully opens at setpoint

No accumulation

Valve remains full open until pressure falls below preset setpoint

valve closes sharply

Blowdown= ((P_setpoint - P_{full closed})/P_setpoint) * 100%

Thermal binding - valve body cools faster than disk which causes binding against valve seat: when valve is closed hot and allowed to cool, it can thermally bind such that re-opening is not possible until valve is reheated

Pressure locking - Liquid becomes trapped in valve bonnet: when bonnet and liquid heats up pressure build-up that occurs can prevent valve operation: valve operation could result in stem or yoke failures.

Valves can be cracked open and reclosed during cooldown.

Use of proper closing torque.

Valve bonnet relief valves.

Kinetic (Dynamic)

Positive Displacement

Cavitation is the formation of vapor bubbles in the eye of a pump and their subsequent collapse on the impeller or in the volute. Cavitation damages pumps due to erosion and pitting that occurs when the vapor bubbles collapse.Has a distinctive sound, fluctuating discharge pressure and motor current.

Prevention is accomplished by reducing the speed of the pump, lowering temperature, increase pressure  throttle discharge valve of a centrifugal pump

Describe the operation of positive displacement pumps, including requirements for the following:

NPSH

Starting a positive displacement pump

Operation with a positive displacement pump deadheaded.

Describe the operation of the following types of positive displacement pumps:

Reciprocating pumps

Rotary pumps

Reciprocating pump operates using a back and forth, straight line motion.

A rotary pump  is a positive displacement pump employing rotary motion.

For a positive displacement pump, Determine the effects of changes in flow, pump speed, pump stroke, or system characteristic curve on the system operating point.

State the purpose of the following centrifugal pump components:

Casing

Gaskets

Impellar

Shaft

Bearings

Seal Rings

Volute

Shaft Seals

Describe the operation fo the following types of centrifugal pumps:

Volute and diffuser pumps

Radial-flow, axial flow, and mixed flow pumps

Describe the operation of centrifugal pumps including requirements for the following:

Operation with a centrifugal pump dead headed

minimum flow

NPSH

Starting a centrifugal pump

Prevention of runout

Draw and label characteristic cuves for centrifugal pump operating modes,

One pump in slow.

One pump in fast

2 in parallel

2 in series

Describe the operation of centrifugal pumps in series and in parallel arrangements