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Geothermal Alliance of IllinoisTXVs – Theory and Fundamentals

John Haug – Senior Application EngineerEmerson Climate Technologies - Flow Controls

Emerson Flow Controls

Anatomy

Operation

Terms & Features

Superheat

Thermal Expansion ValveTopics


Internal Check (Optional)

Superheat Spring

Sensing Bulb

Thermal Expansion ValveAnatomy

Power Element

Metering Pin

Valve Inlet

Diaphragm

Valve Packing

Pin Carrier

Valve Outlet

S.H. AdjustingStem (Optional)

External Equalizer


ThermalBallast

Thermal Expansion ValvePower Assembly

DiaphragmStainless Steel

ThermalBallast

Buffer Plate

StainlessSteel P.E.


Thermal Expansion ValveMetering Pin & Port

Metering Pin

Valve Port

Valve Inlet

Pin Carrier

Valve Outlet


Anatomy

Operation

Terms & Features

Superheat



Why Do You Need A … TXV

“It regulates the flow of liquid refrigerant into the coil to match the heat load on the coil”.

This is accomplished by controlling the superheat temperature of the refrigerant vapor leaving the coil.


Purpose Of A TXV

– Responds To Temperature And Pressure Only

Does Not Control:– Space Temperature – Head Pressure– Capacity– Suction Pressure– Humidity

Controls Evaporator Superheat


Thermal Expansion ValveValve Operation (Separates high side from low side)

HighPressureLiquid

Low Pressure Liquid and Vapor


HighPressureLiquid

Low Pressure Liquid and Vapor

100°F

40°F

Thermal Expansion ValveValve Operation

100°F

40°F


P1Remote Bulb And Power Assembly Pressure(Only Opening Force) P2

Evaporator Pressure (Closing Force)

P3 Superheat Spring(Closing Force)

Valve is in Balance When

P1=P2+P3

Thermal Expansion ValveValve Operation


Anatomy

Operation

Superheat

Terms & Features



1 pound ofWater 72˚


1 pound ofSteam 212˚




+ 140 BTU =(Sensible Heat)

+ 970 BTU =(Latent Heat)

+ 8 BTU = (Sensible Heat)


10°F Superheat 10°F Superheat

+ 40

+ 50

- 40

- 30

Superheat Is A Temperature DifferenceNot Just A Temperature


68.5 PSIG = 40 F

65.6 PSIG = 38 F

58.5 PSIG = 33 F

Saturated Suction Pressure 58.5 PSIG

P TCHART

33°F

40°FActual Temp.

Actual Superheat = 7°F

R-22Superheat Measurement

Note: Turn ClockwiseTo Increase S/H


Thermal Expansion Valves Normal Superheat Settings

High Temp = 10 to 12 F (>30°F Evap. )

Medium Temp = 5 to 10 F (0 to 30°F Evap.)

Low Temp = 2 to 5 F (Below 0°F Evap.)

Follow System Manufacturers Recommended Superheat


Turn Adjustment Stem Clockwise To Increase Superheat.

Adjustment (Superheat Change) Varies By:– Valve manufacturer– Valve family– Refrigerant– Evaporator Temperature

Thermal Expansion Valves Superheat Adjustments

NXT


Anatomy

Operation

Superheat

Terms & Features



Thermal Expansion ValveFixed Vs Adjustable Superheat


InternalEqualizer

ExternalEqualizer

Thermal Expansion ValveInternal Vs External Equalizers

Outlet Connection

Separate Equalizer Connection


Allows High And Low Side System Pressures To Equalize During The Off Cycle Thereby Allowing The Use Of Low Start Torque Compressors

Adds To Total Valve Capacity 15% To 20% Typical Bleed Rate

A Bleed Port Is An Internal Passage Directly Between The Valve Inlet And Outlet.

Thermal Expansion ValveInternal Bleed Option


Water Source HP Bi-Flow Cooling


Water Source HP Bi-Flow Heating


FlowFlow

Thermal Expansion ValveInternal Check Option

Forward (Closed) Flow(Low Leak)

Reverse (Open) Flow(High Flow)


Water Source HP Dual TXVs Cooling


Water Source HP Dual TXVs Heating

http://www.emersonclimate.com

• Emerson valves, controls and system protectors.

• Other Emerson products including Copeland compressors and White-Rogers thermostats.

• Additional training and educational material.

TXV Troubleshooting


Bulb Should Be Clamp On A Horizontal Run Bulb Should Be Locate On The Pipe At:

– 12 O’clock On Less Than 7/8" Pipe– 8 Or 4 O’clock On Greater Than 7/8" Pipe

In All Cases The Bulb Should Be Insulated From The Ambient

Sensing Bulb Location

8 O’clock 4 O’clock

12 O’clock


In Most Cases The Bulb Can Be Mounted In Any Position On A Vertical Run

In Most Cases It Is Not True That The Charge Will Leave Bulb If Mounted With Cap Tube Down

Why Not OK?

Horizontal Position Is Preferred

Sensing Bulb Location

OK

NotOK


The Bulb Should Be Located As Close As Possible To The Outlet Of The Evaporator Outlet

The Bulb Should Be As Close As Possible To The Equalizer Tube

The Bulb Should Be Located Up Stream Of The Equalizer To Prevent Being Effected By Any Liquid Leakage Through The Equalizer Tube

Proper Bulb and Equalizer Location


The Bulb Should Not Be Mounted On The Evaporator Suction Header

The Bulb Can Not Measure The Temperature On The Bottom Runs– This Could Create A Possible Flood Back

Situation

Improper Bulb and Equalizer Location


If The Bulb And The Equalizer Are Not On The Same Side Of The P Trap Poor Superheat Control Can Result– Equalizer On The Coil Side Can Result In High

Superheat– Bulb On The Coil Side Can Result In Low

Superheat


WRONG


If A P-Trap Is Used The Equalizer And The Bulb Have To Be On The Same Side Of The Trap– Coil Side Is

Preferred– If There Is Not

Enough Room The Compressor Side Of The Trap Will Work



Valve Doesn’t Feed Enough

Corrective Action: Add Refrigerant

No Solid Column Of Liquid – Valve Can’t Make

Capacity Results

– High Superheat– Loss of Coil Efficiency

The Valve Must Have a Solid Column of Liquid at the Inlet


Flash Gas Bubbles At

TXV Inlet0


Corrective Action: Remove Source Of Restriction Or Add Refrigerant

Cause: Flash Gas In The Liquid Line

Diagnose By: Look For Flash Gas In The Sight

Glass Listen For A Whistling Sound At

The TXV.

Results:– High Superheat– Loss Of Coil Efficiency


Last Point of Refrigerant

Normal Setting


Corrective Action: Change Superheat Setting

Cause: Incorrect Superheat Setting (High)

High Setting

Inefficient

Last Point of Liquid Refrigerant


The Loss Of P1 Means The Only Opening Force In The Valve Has Disappeared.

This Means Little Or No Flow Through The Valve - High Superheat

Diagnose: Remove Bulb And Hold In Your Hand

– If No Change In Valve Flow, Then The Bulb Has Lost Charge


Corrective Action: Replace Power Head Or Valve

Cause: Low or Lost Bulb Charge P1

P2

P3


Bulb Location– Reposition Bulb

Too Large A Valve– Replace Valve With The Proper Size

Superheat Adjustment– Adjust Superheat To Correct Setting

Don’t Jump to Conclusions to Quickly– If the valve has been operating properly for a lengthy period

of time it’s probably not the conclusions listed above

Superheat Is Erratic Or Hunts


TXV TroubleshootingProblem Sympton Cause Fix

OverfeedingOverfeedingOverfeedingOverfeedingOverfeeding

Low Superheat S/H SettingOversize TXVOverchargeBulb LocationDirty Evaporator

AdjustReplaceRemove Refrig.RelocateClean

UnderfeedingUnderfeedingUnderfeedingUnderfeedingUnderfeeding

High Superheat S/H SettingUnderchargeDamaged Power HeadClogged DrierIce Forming

AdjustAdd Refrig.ReplaceChangeChange Drier

HuntingHuntingHunting

Fluctuating S/H Bulb LocationOversize TXVS/H Setting

RelocateReplaceAdjust

(See catalog section for more)

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