ASHRAE Journal - February 2020 - 40

CELEBRATING 125 YEARS

History of Thermostatic
Expansion Valve
BY JORDAN C. LARSEN; BRIGITTE BUSCH

A thermostatic expansion valve (TXV)-an example of which can be seen in Figure 1-
is a refrigeration and air conditioning throttling device that controls the amount of
refrigerant liquid injected into a system's evaporator based on the evaporator outlet
temperature and pressure, called the superheat.¹ Figure 2 shows the different phases
and pressures the refrigerant goes through as it is pumped through the system,
moving through the evaporator, the compressor, the condenser, and the throttling
device which injects liquid refrigerant into the evaporator before it evaporates and
moves into the compressor.
TXV Parts
While there are different types of TXVs, each one has
some things in common: a diaphragm, a power element, a setting spring and an oriﬁce (Figure 3).

TXV Operation
There are three different forces at work in a TXV: bulb
pressure, spring pressure and evaporator pressure
(Figure 4). Bulb pressure comes from the bulb that is
mounted at the outlet of the evaporator. The bulb senses
the suction temperature, which generates an internal
pressure in the bulb that drives the diaphragm down
when the temperature increases. Spring pressure is
constant and pushes up against the diaphragm, counter
to the bulb pressure. The spring pressure is calibrated
when the valve is set by the equipment manufacturer
or the installer. The evaporator pressure pushes the
diaphragm up when the suction pressure increases and

comes from the evaporator load on the system, which
varies according to different operating conditions,
such as changing load conditions. Based on the balance
between these three pressures, the valve will either
open or close.

Factors That Led to the Development of the TXV
Many early refrigeration systems required a human
operator2 to constantly adjust the ﬂow of refrigeration
to prevent liquid refrigerant from ﬂowing back into the
compressor, which would cause irreparable damage. To
properly address this challenge, an automatic refrigerant control was needed. Harry Thompson ﬁled the ﬁrst
patent3 for a TXV on August 24, 1927 (Figure
( igure 5).
5). With
Thompson's invention, refrigeration systems now had an
automated throttling device that also protected against
liquid refrigerant ﬂowing back into the compressor.
Thompson's invention was so successful that he

Jordan C. Larsen is a technical writer and editor for Danfoss North America. Brigitte Busch is a product manager for Danfoss Cooling.
40

ASHRAE JOURNAL

ashrae.org

FEBRUARY 2020

https://www.ashrae.org/

ASHRAE Journal - February 2020

Table of Contents for the Digital Edition of ASHRAE Journal - February 2020

Contents
ASHRAE Journal - February 2020 - Intro
ASHRAE Journal - February 2020 - Cover1
ASHRAE Journal - February 2020 - Cover2
ASHRAE Journal - February 2020 - Cover2a
ASHRAE Journal - February 2020 - Contents
ASHRAE Journal - February 2020 - 3
ASHRAE Journal - February 2020 - 4
ASHRAE Journal - February 2020 - 5
ASHRAE Journal - February 2020 - 6
ASHRAE Journal - February 2020 - 7
ASHRAE Journal - February 2020 - 8
ASHRAE Journal - February 2020 - 9
ASHRAE Journal - February 2020 - 10
ASHRAE Journal - February 2020 - 11
ASHRAE Journal - February 2020 - 12
ASHRAE Journal - February 2020 - 13
ASHRAE Journal - February 2020 - 14
ASHRAE Journal - February 2020 - 15
ASHRAE Journal - February 2020 - 16
ASHRAE Journal - February 2020 - 17
ASHRAE Journal - February 2020 - 18
ASHRAE Journal - February 2020 - 19
ASHRAE Journal - February 2020 - 20
ASHRAE Journal - February 2020 - 21
ASHRAE Journal - February 2020 - 22
ASHRAE Journal - February 2020 - 23
ASHRAE Journal - February 2020 - 24
ASHRAE Journal - February 2020 - 25
ASHRAE Journal - February 2020 - 26
ASHRAE Journal - February 2020 - 27
ASHRAE Journal - February 2020 - 28
ASHRAE Journal - February 2020 - 29
ASHRAE Journal - February 2020 - 30
ASHRAE Journal - February 2020 - 31
ASHRAE Journal - February 2020 - 32
ASHRAE Journal - February 2020 - 33
ASHRAE Journal - February 2020 - 34
ASHRAE Journal - February 2020 - 35
ASHRAE Journal - February 2020 - 36
ASHRAE Journal - February 2020 - 37
ASHRAE Journal - February 2020 - 38
ASHRAE Journal - February 2020 - 39
ASHRAE Journal - February 2020 - 40
ASHRAE Journal - February 2020 - 41
ASHRAE Journal - February 2020 - 42
ASHRAE Journal - February 2020 - 43
ASHRAE Journal - February 2020 - 44
ASHRAE Journal - February 2020 - 45
ASHRAE Journal - February 2020 - 46
ASHRAE Journal - February 2020 - 47
ASHRAE Journal - February 2020 - 48
ASHRAE Journal - February 2020 - 49
ASHRAE Journal - February 2020 - 50
ASHRAE Journal - February 2020 - 51
ASHRAE Journal - February 2020 - 52
ASHRAE Journal - February 2020 - 53
ASHRAE Journal - February 2020 - 54
ASHRAE Journal - February 2020 - 55
ASHRAE Journal - February 2020 - 56
ASHRAE Journal - February 2020 - 57
ASHRAE Journal - February 2020 - 58
ASHRAE Journal - February 2020 - 59
ASHRAE Journal - February 2020 - 60
ASHRAE Journal - February 2020 - 61
ASHRAE Journal - February 2020 - 62
ASHRAE Journal - February 2020 - 63
ASHRAE Journal - February 2020 - 64
ASHRAE Journal - February 2020 - 65
ASHRAE Journal - February 2020 - 66
ASHRAE Journal - February 2020 - 67
ASHRAE Journal - February 2020 - 68
ASHRAE Journal - February 2020 - 69
ASHRAE Journal - February 2020 - 70
ASHRAE Journal - February 2020 - 71
ASHRAE Journal - February 2020 - 72
ASHRAE Journal - February 2020 - 73
ASHRAE Journal - February 2020 - 74
ASHRAE Journal - February 2020 - 75
ASHRAE Journal - February 2020 - 76
ASHRAE Journal - February 2020 - 77
ASHRAE Journal - February 2020 - 78
ASHRAE Journal - February 2020 - 79
ASHRAE Journal - February 2020 - 80
ASHRAE Journal - February 2020 - Cover3
ASHRAE Journal - February 2020 - Cover4
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_FYONLJ
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2024november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2024november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_BDMHLG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WJDGRY
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ATMAHK
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_VHQRAW
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XGMDXI
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_YELQLJ
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QJLWMC
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_MCDEBX
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WNYSQY
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XATVOD
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_FJSHSS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_CCBZDS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XDEFVG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2023november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2023november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_VHGNBL
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WPKBNJ
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_UUVCDE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RTGDEW
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2023
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_LKRFXS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_AZSOFG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ERCDBH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QWDFRV
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JHGVDF
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OPUYHG
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SREIBM
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_LRTGLK
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OKRFGH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2022november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2022november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_TZSERA
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_LVRUIX
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RPTVYZ
https://www.nxtbook.com/nxtbooks/ashrae/mini_pub_catalog
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XIYTGD
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2022
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RFGDOB
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_PABXNU
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_REMKLS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_PICVBT
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_AOYTVW
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JQOPLS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_IOYTBC
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SGAJJF
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_IGHYER
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_PDRKLS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2021november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2021november_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_XCODFR
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QSLFGO
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ILKVNM
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2021
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OPDJKD
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_VJKSRY
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SDHUTC
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JPPKRR
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SDLTTH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_CKLLES
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_SLDOX
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_HJETUK
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_OLUHGE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2020october
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2020october_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ZERDGH
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_QVMNEO
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_RTPOKE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_BBATRE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_STUBMW
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_TPEMPE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_JNMKDS
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_FBTTPA
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_WQMMNE
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_TVBRYN
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_showguide2020
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_KTUZMA
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ABEDGD
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201910
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201909
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2019septmeber_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2019september
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201908
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201907
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201906
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201905
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201904
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2019april
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201903
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2019march
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201902
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201901
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_showguide2019
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018december
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018november
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2018fall_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2018fall
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018october
https://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2018
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201810
https://www.nxtbook.com/nxtbooks/ashrae/ashraeinsights_201806
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201805
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201804
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201803
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201712
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201711
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201710
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2017fall_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2017fall
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201709
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201705
https://www.nxtbook.com/nxtbooks/ashrae/ashrae_meetinginsert_201610
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2016fall_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2016fall
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acrexindia
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2015summer_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2015summer
https://www.nxtbook.com/nxtbooks/amca/2014summer2
https://www.nxtbook.com/nxtbooks/amca/2014summer
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acma_2014summer
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201311
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201309
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acmasupp_2013fall
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201305
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201303
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2013winter
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201211
https://www.nxtbook.com/nxtbooks/ashrae/achr_expo_mexico2012
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201209
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201208_v3
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201208_v2
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2012summer
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201205
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201203
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2012winter
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201111_v2
https://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201109_v2
https://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2011summer
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201105
https://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201103
https://www.nxtbookmedia.com