Apollo command module oxygen - Revision history

Flerf Whisperer: Photograph of the service module oxygen tank the command module drew from

2026-10-14T00:36:45Z

Photograph of the service module oxygen tank the command module drew from

← Older revision		Revision as of 20:36, 13 October 2026
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	== From the service module ==		== From the service module ==
			<div style="float:right; width:320px; margin:0.15em 0 0.8em 1.15em; clear:right;">
			[[File:Apollo service module oxygen tank Stafford dsc46598 small.jpg\|link=File:Apollo service module oxygen tank Stafford dsc46598 full.jpg]]
			<div style="font-size:13px; line-height:1.35; margin-top:6px;">Service module cryogenic oxygen tank, serial 10024XTA0051, in its shipping container at the Stafford Air and Space Museum. This is the tank the command module drew from. The surge tank inside the command module is a smaller bottle. Photo: [http://heroicrelics.org/stafford/apollo-o2-tank/dsc46598.jpg.html Mike Jetzer/heroicrelics.org].</div>
			</div>
	The oxygen subsystem shared its supply with the fuel cells. The 1969 handbook states it this way:		The oxygen subsystem shared its supply with the fuel cells. The 1969 handbook states it this way:

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	The tanks were filled before launch and were not changed in flight. The command module had no spare tank to bolt in.		The tanks were filled before launch and were not changed in flight. The command module had no spare tank to bolt in.

			<div style="clear:both;"></div>
	== Warming on the glycol line ==		== Warming on the glycol line ==
	The water-glycol loop, what it cooled, and the radiators on the service module are on [[Apollo command module cooling]].		The water-glycol loop, what it cooled, and the radiators on the service module are on [[Apollo command module cooling]].

Flerf Whisperer: Link the cooling article from the glycol warmer

2026-10-13T23:25:56Z

Link the cooling article from the glycol warmer

← Older revision		Revision as of 19:25, 13 October 2026
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	== Warming on the glycol line ==		== Warming on the glycol line ==
			The water-glycol loop, what it cooled, and the radiators on the service module are on [[Apollo command module cooling]].


	<div style="clear:both; margin:0.6em auto 1.2em; max-width:640px; text-align:center;">		<div style="clear:both; margin:0.6em auto 1.2em; max-width:640px; text-align:center;">
	[[File:Apollo CM oxygen glycol schematic small.jpg\|link=File:Apollo CM oxygen glycol schematic full.jpg]]		[[File:Apollo CM oxygen glycol schematic small.jpg\|link=File:Apollo CM oxygen glycol schematic full.jpg]]
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	== See also ==		== See also ==
			* [[Apollo command module cooling]]
	* [[Apollo oxygen]]		* [[Apollo oxygen]]
	* [[Apollo lunar module oxygen]]		* [[Apollo lunar module oxygen]]

Washcarso at 23:18, 13 October 2026

2026-10-13T23:18:50Z

← Older revision		Revision as of 19:18, 13 October 2026
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	<references />		<references />

	[[Category:Apollo ~~program~~]]		[[Category:Apollo oxygen]]
	[[Category:Apollo evidence]]		[[Category:Apollo evidence]]
	[[Category:Moon]]		[[Category:Moon]]
	[[Category:Spaceflight]]		[[Category:Spaceflight]]

Washcarso at 23:51, 12 October 2026

2026-10-12T23:51:13Z

← Older revision		Revision as of 19:51, 12 October 2026
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			{{series apollo}}

	The '''command module oxygen system''' took oxygen from the service module at about 900 [[Pounds per square inch\|psi]], warmed it, stored a small reserve in the command module, and stepped the pressure down to about 5 [[Pounds per square inch\|psi]] for the crew. The tanks themselves stayed in the service module. What follows is the plumbing on the command-module side of that line: the capillaries on the water-glycol line, the surge tank, the regulators, the suit loop, and the lithium hydroxide beds.		The '''command module oxygen system''' took oxygen from the service module at about 900 [[Pounds per square inch\|psi]], warmed it, stored a small reserve in the command module, and stepped the pressure down to about 5 [[Pounds per square inch\|psi]] for the crew. The tanks themselves stayed in the service module. What follows is the plumbing on the command-module side of that line: the capillaries on the water-glycol line, the surge tank, the regulators, the suit loop, and the lithium hydroxide beds.

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	<references />		<references />

			[[Category:Apollo program]]
	[[Category:Apollo evidence]]		[[Category:Apollo evidence]]
	[[Category:Moon]]		[[Category:Moon]]
	[[Category:Spaceflight]]		[[Category:Spaceflight]]

Flerf Whisperer: Link the lunar module oxygen page

2026-10-12T19:02:52Z

Link the lunar module oxygen page

← Older revision		Revision as of 15:02, 12 October 2026
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	== See also ==		== See also ==
	* [[Apollo oxygen]]		* [[Apollo oxygen]]
			* [[Apollo lunar module oxygen]]
	* [[Pounds per square inch]]		* [[Pounds per square inch]]
	* [[Moon landings]]		* [[Moon landings]]

Flerf Whisperer: Add the descent and postlanding steps that bring the cabin back to sea-level pressure

2026-10-12T18:20:53Z

Add the descent and postlanding steps that bring the cabin back to sea-level pressure

@@ Line 138: / Line 138: @@
 <div style="font-size:13px; line-height:1.35; margin-top:6px;">The mailbox prototype in Mission Control, 15 April 1970, with a command-module lithium hydroxide canister on a suit hose. NASA S70-35013.</div>
 </div>
 == See also ==

Flerf Whisperer: Call the suit relief a pressure in inches of water column, and link psi, psia, and psig

2026-10-12T18:03:40Z

Call the suit relief a pressure in inches of water column, and link psi, psia, and psig

Show changes

Flerf Whisperer: Float the coolant control panel beside the Apollo 14 flow paragraph, and put the unit side view back in the suit loop

2026-10-12T17:42:56Z

Float the coolant control panel beside the Apollo 14 flow paragraph, and put the unit side view back in the suit loop

← Older revision		Revision as of 13:42, 12 October 2026
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	<blockquote>Oxygen delivery to the ECS at 900 ± 35 psia is limited to 4.5 lb/hr from each tank by the combination flow restrictors and heat exchangers, which ensure a minimum temperature of 0°F at the maximum flow rate.<ref name="csm" /></blockquote>		<blockquote>Oxygen delivery to the ECS at 900 ± 35 psia is limited to 4.5 lb/hr from each tank by the combination flow restrictors and heat exchangers, which ensure a minimum temperature of 0°F at the maximum flow rate.<ref name="csm" /></blockquote>

	<div style="float:right; width:~~200px~~; margin:0.15em 0 0.6em 1.25em;">		<div style="float:right; width:240px; margin:0.15em 0 0.6em 1.25em;">
	[[File:Apollo CM ~~ECU left side~~ small.jpg\|link=File:Apollo CM ~~ECU left side~~ full.jpg]]		[[File:Apollo CM coolant control panel small.jpg\|link=File:Apollo CM coolant control panel full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">~~Environmental~~ control unit~~, left side~~. ~~Demand regulator at the top, cabin return~~ in ~~the middle, coolant panel below~~. Photograph by Steve Jurvetson, 2020.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px;">Coolant control panel on a Block II environmental control unit. The capillaries were wound on a line in this system. Photograph by Steve Jurvetson, 2020.</div>
	</div>		</div>
	A third document, the Apollo 14 command-module news reference, sets the pair at 9 pounds an hour, to prevent starvation of the fuel cells, and again says the capillaries heat the oxygen so it does not enter as a liquid.<ref name="csm14">[https://apollojournals.org/alsj/CSM14_Environmental_Control_Subsystem_pp117-136.pdf Environmental control subsystem], Apollo command and service module news reference, Apollo Lunar Surface Journal.</ref> The three sources agree on the method. They do not agree on the flow number: 7.5 pounds an hour for the pair, 4.5 pounds an hour from each tank, or 9 pounds an hour for the pair.		A third document, the Apollo 14 command-module news reference, sets the pair at 9 pounds an hour, to prevent starvation of the fuel cells, and again says the capillaries heat the oxygen so it does not enter as a liquid.<ref name="csm14">[https://apollojournals.org/alsj/CSM14_Environmental_Control_Subsystem_pp117-136.pdf Environmental control subsystem], Apollo command and service module news reference, Apollo Lunar Surface Journal.</ref> The three sources agree on the method. They do not agree on the flow number: 7.5 pounds an hour for the pair, 4.5 pounds an hour from each tank, or 9 pounds an hour for the pair.
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	The capillaries are the restriction that chills the gas as it expands, and the glycol line under the coil is what puts the heat back. The spacecraft 012 handbook is explicit about which glycol line, and about what happens if that line is cold during a cabin refill:		The capillaries are the restriction that chills the gas as it expands, and the glycol line under the coil is what puts the heat back. The spacecraft 012 handbook is explicit about which glycol line, and about what happens if that line is cold during a cabin refill:

	~~<div style="clear:right; float:right; width:240px; margin:0.15em 0 0.6em 1.25em;">~~
	~~[[File:Apollo CM coolant control panel small.jpg\|link=File:Apollo CM coolant control panel full.jpg]]~~
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">Coolant control panel on a Block II environmental control unit. The capillaries were wound on a line in this system. Photograph by Steve Jurvetson, 2020.</div>
	~~</div>~~
	<blockquote>To insure proper operation of the oxygen supply restrictors, in the line between the cryogenic O<sub>2</sub> storage in the S/M to the surge tanks in the C/M during cabin repressurization, full water-glycol flow through the line to the space radiators is required. Sufficient heat must be available to prevent cryogenic oxygen entering the C/M oxygen system and preclude the possibility of freezing the water-glycol. To achieve this, the mixing valve must be manually placed to the full closed position 15 to 30 minutes before repressurization and remain closed until the surge tank returns to maximum pressure after repressurization of the C/M.<ref name="sc012" /></blockquote>		<blockquote>To insure proper operation of the oxygen supply restrictors, in the line between the cryogenic O<sub>2</sub> storage in the S/M to the surge tanks in the C/M during cabin repressurization, full water-glycol flow through the line to the space radiators is required. Sufficient heat must be available to prevent cryogenic oxygen entering the C/M oxygen system and preclude the possibility of freezing the water-glycol. To achieve this, the mixing valve must be manually placed to the full closed position 15 to 30 minutes before repressurization and remain closed until the surge tank returns to maximum pressure after repressurization of the C/M.<ref name="sc012" /></blockquote>

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	<blockquote>When the pressure drops approximately 3-inch H<sub>2</sub>O pressure below cabin, the diaphragm will open the demand valve.<ref name="aoh" /></blockquote>		<blockquote>When the pressure drops approximately 3-inch H<sub>2</sub>O pressure below cabin, the diaphragm will open the demand valve.<ref name="aoh" /></blockquote>

			<div style="clear:right; float:right; width:200px; margin:0.15em 0 0.6em 1.25em;">
			[[File:Apollo CM ECU left side small.jpg\|link=File:Apollo CM ECU left side full.jpg]]
			<div style="font-size:13px; line-height:1.35; margin-top:6px;">The same corner: demand regulator at the top, cabin return in the middle, coolant panel below. Photograph by Steve Jurvetson, 2020.</div>
			</div>
	A relief valve in the same assembly vents the suits if they rise to between 2 and 9 inches of water above the cabin. The flight report's table says the regulator supplies oxygen when the suit circuit is 3.0 inches of water, within 0.5 inch, below cabin pressure, and relieves when the suit is 2 inches of water above the cabin.<ref name="csm" /> The suits stay just under cabin pressure, so they do not balloon.		A relief valve in the same assembly vents the suits if they rise to between 2 and 9 inches of water above the cabin. The flight report's table says the regulator supplies oxygen when the suit circuit is 3.0 inches of water, within 0.5 inch, below cabin pressure, and relieves when the suit is 2 inches of water above the cabin.<ref name="csm" /> The suits stay just under cabin pressure, so they do not balloon.

Flerf Whisperer: Move the environmental control unit side view up to the Apollo 14 flow paragraph

2026-10-12T17:39:58Z

Move the environmental control unit side view up to the Apollo 14 flow paragraph

← Older revision		Revision as of 13:39, 12 October 2026
Line 39:		Line 39:
	<blockquote>Oxygen delivery to the ECS at 900 ± 35 psia is limited to 4.5 lb/hr from each tank by the combination flow restrictors and heat exchangers, which ensure a minimum temperature of 0°F at the maximum flow rate.<ref name="csm" /></blockquote>		<blockquote>Oxygen delivery to the ECS at 900 ± 35 psia is limited to 4.5 lb/hr from each tank by the combination flow restrictors and heat exchangers, which ensure a minimum temperature of 0°F at the maximum flow rate.<ref name="csm" /></blockquote>

			<div style="float:right; width:200px; margin:0.15em 0 0.6em 1.25em;">
			[[File:Apollo CM ECU left side small.jpg\|link=File:Apollo CM ECU left side full.jpg]]
			<div style="font-size:13px; line-height:1.35; margin-top:6px;">Environmental control unit, left side. Demand regulator at the top, cabin return in the middle, coolant panel below. Photograph by Steve Jurvetson, 2020.</div>
			</div>
	A third document, the Apollo 14 command-module news reference, sets the pair at 9 pounds an hour, to prevent starvation of the fuel cells, and again says the capillaries heat the oxygen so it does not enter as a liquid.<ref name="csm14">[https://apollojournals.org/alsj/CSM14_Environmental_Control_Subsystem_pp117-136.pdf Environmental control subsystem], Apollo command and service module news reference, Apollo Lunar Surface Journal.</ref> The three sources agree on the method. They do not agree on the flow number: 7.5 pounds an hour for the pair, 4.5 pounds an hour from each tank, or 9 pounds an hour for the pair.		A third document, the Apollo 14 command-module news reference, sets the pair at 9 pounds an hour, to prevent starvation of the fuel cells, and again says the capillaries heat the oxygen so it does not enter as a liquid.<ref name="csm14">[https://apollojournals.org/alsj/CSM14_Environmental_Control_Subsystem_pp117-136.pdf Environmental control subsystem], Apollo command and service module news reference, Apollo Lunar Surface Journal.</ref> The three sources agree on the method. They do not agree on the flow number: 7.5 pounds an hour for the pair, 4.5 pounds an hour from each tank, or 9 pounds an hour for the pair.

	The capillaries are the restriction that chills the gas as it expands, and the glycol line under the coil is what puts the heat back. The spacecraft 012 handbook is explicit about which glycol line, and about what happens if that line is cold during a cabin refill:		The capillaries are the restriction that chills the gas as it expands, and the glycol line under the coil is what puts the heat back. The spacecraft 012 handbook is explicit about which glycol line, and about what happens if that line is cold during a cabin refill:

	<div style="float:right; width:240px; margin:0.15em 0 0.6em 1.25em;">		<div style="clear:right; float:right; width:240px; margin:0.15em 0 0.6em 1.25em;">
	[[File:Apollo CM coolant control panel small.jpg\|link=File:Apollo CM coolant control panel full.jpg]]		[[File:Apollo CM coolant control panel small.jpg\|link=File:Apollo CM coolant control panel full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">Coolant control panel on a Block II environmental control unit. The capillaries were wound on a line in this system. Photograph by Steve Jurvetson, 2020.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px;">Coolant control panel on a Block II environmental control unit. The capillaries were wound on a line in this system. Photograph by Steve Jurvetson, 2020.</div>
Line 92:		Line 96:
	<blockquote>When the pressure drops approximately 3-inch H<sub>2</sub>O pressure below cabin, the diaphragm will open the demand valve.<ref name="aoh" /></blockquote>		<blockquote>When the pressure drops approximately 3-inch H<sub>2</sub>O pressure below cabin, the diaphragm will open the demand valve.<ref name="aoh" /></blockquote>

	~~<div style="clear:right; float:right; width:200px; margin:0.15em 0 0.6em 1.25em;">~~
	~~[[File:Apollo CM ECU left side small.jpg\|link=File:Apollo CM ECU left side full.jpg]]~~
	~~<div style="font-size:13px; line-height:1.35; margin-top:6px;">The same corner: demand regulator at the top, cabin return in the middle, coolant panel below. Photograph by Steve Jurvetson, 2020.</div>~~
	~~</div>~~
	A relief valve in the same assembly vents the suits if they rise to between 2 and 9 inches of water above the cabin. The flight report's table says the regulator supplies oxygen when the suit circuit is 3.0 inches of water, within 0.5 inch, below cabin pressure, and relieves when the suit is 2 inches of water above the cabin.<ref name="csm" /> The suits stay just under cabin pressure, so they do not balloon.		A relief valve in the same assembly vents the suits if they rise to between 2 and 9 inches of water above the cabin. The flight report's table says the regulator supplies oxygen when the suit circuit is 3.0 inches of water, within 0.5 inch, below cabin pressure, and relieves when the suit is 2 inches of water above the cabin.<ref name="csm" /> The suits stay just under cabin pressure, so they do not balloon.

Flerf Whisperer: Place the photos in the text: floats beside the passages they illustrate, even rows, captions that line up

2026-10-12T17:31:03Z

Place the photos in the text: floats beside the passages they illustrate, even rows, captions that line up

← Older revision		Revision as of 13:31, 12 October 2026
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	The capillaries are the restriction that chills the gas as it expands, and the glycol line under the coil is what puts the heat back. The spacecraft 012 handbook is explicit about which glycol line, and about what happens if that line is cold during a cabin refill:		The capillaries are the restriction that chills the gas as it expands, and the glycol line under the coil is what puts the heat back. The spacecraft 012 handbook is explicit about which glycol line, and about what happens if that line is cold during a cabin refill:

			<div style="float:right; width:240px; margin:0.15em 0 0.6em 1.25em;">
			[[File:Apollo CM coolant control panel small.jpg\|link=File:Apollo CM coolant control panel full.jpg]]
			<div style="font-size:13px; line-height:1.35; margin-top:6px;">Coolant control panel on a Block II environmental control unit. The capillaries were wound on a line in this system. Photograph by Steve Jurvetson, 2020.</div>
			</div>
	<blockquote>To insure proper operation of the oxygen supply restrictors, in the line between the cryogenic O<sub>2</sub> storage in the S/M to the surge tanks in the C/M during cabin repressurization, full water-glycol flow through the line to the space radiators is required. Sufficient heat must be available to prevent cryogenic oxygen entering the C/M oxygen system and preclude the possibility of freezing the water-glycol. To achieve this, the mixing valve must be manually placed to the full closed position 15 to 30 minutes before repressurization and remain closed until the surge tank returns to maximum pressure after repressurization of the C/M.<ref name="sc012" /></blockquote>		<blockquote>To insure proper operation of the oxygen supply restrictors, in the line between the cryogenic O<sub>2</sub> storage in the S/M to the surge tanks in the C/M during cabin repressurization, full water-glycol flow through the line to the space radiators is required. Sufficient heat must be available to prevent cryogenic oxygen entering the C/M oxygen system and preclude the possibility of freezing the water-glycol. To achieve this, the mixing valve must be manually placed to the full closed position 15 to 30 minutes before repressurization and remain closed until the surge tank returns to maximum pressure after repressurization of the C/M.<ref name="sc012" /></blockquote>

	Closing the mixing valve sends warm coolant, rather than coolant just back from the radiators, through the line the capillaries are wound on.		Closing the mixing valve sends warm coolant, rather than coolant just back from the radiators, through the line the capillaries are wound on. The water-glycol hardware lived in the environmental control unit in the left-hand equipment bay, together with the suit loop. The panel in the photograph sets primary and secondary glycol to the suit heat exchangers, and it sets the glycol evaporator. No public photograph shows the capillary coil itself. It is drawn on the handbook schematic above, and it is described in the sentences quoted here. The round vessels on the same unit are part of that environmental control package. The 900 psi oxygen surge tank was a separate bottle beside the unit.<ref name="aoh" /><ref name="csm" />

	~~<div style="clear:both; margin:1em auto 1.2em; max-width:240px; text-align:center;">~~
	~~[[File:Apollo CM coolant control panel small.jpg\|link=File:Apollo CM coolant control panel full.jpg]]~~
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">Coolant control panel on a Block II environmental control unit. The oxygen capillaries were wound on a line in this coolant system. They are not visible here. Photograph by Steve Jurvetson, 2020.</div>
	~~</div>~~
	The water-glycol hardware lived in the environmental control unit in the left-hand equipment bay, together with the suit loop. The panel in the photograph sets primary and secondary glycol to the suit heat exchangers, and it sets the glycol evaporator. No public photograph shows the capillary coil itself. It is drawn on the handbook schematic above, and it is described in the sentences quoted here. The round vessels on the same unit are part of that environmental control package. The 900 psi oxygen surge tank was a separate bottle beside the unit.<ref name="aoh" /><ref name="csm" />

			<div style="clear:both;"></div>
	== High-pressure oxygen in the command module ==		== High-pressure oxygen in the command module ==
	After the check valves, the two inlet lines joined. The 1969 handbook sends that single line to the oxygen service-module supply valve on panel 326, which was closed before the command module separated from the service module.<ref name="aoh" /> From there the oxygen was still near 900 psi. It went, in parallel, to the surge tank and to the main regulator.		After the check valves, the two inlet lines joined. The 1969 handbook sends that single line to the oxygen service-module supply valve on panel 326, which was closed before the command module separated from the service module.<ref name="aoh" /> From there the oxygen was still near 900 psi. It went, in parallel, to the surge tank and to the main regulator.
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	<div style="float:right; width:260px; margin:0 0 0.8em 1.1em;">		<div style="float:right; width:260px; margin:0 0 0.8em 1.1em;">
	[[File:Apollo CM panel 380 small.jpg\|link=File:Apollo CM panel 380 full.jpg]]		[[File:Apollo CM panel 380 small.jpg\|link=File:Apollo CM panel 380 full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">Panel 380, ~~stenciled as~~ the oxygen demand regulator. The handle selects BOTH or OFF. ~~Above it is the suit test valve. Photograph from the spaceaholic~~ collection, 2010.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px;">Panel 380, the oxygen demand regulator. The handle selects BOTH or OFF. Spaceaholic collection, 2010.</div>
	</div>		</div>
	The demand regulator sits on panel 380, on the environmental control unit. It is the regulator the crew could reach. The handbook puts it there, and the stencil on the hardware says the same thing.<ref name="aoh" />		The demand regulator sits on panel 380, on the environmental control unit. It is the regulator the crew could reach. The handbook puts it there, and the stencil on the hardware says the same thing.<ref name="aoh" />
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	<blockquote>When the pressure drops approximately 3-inch H<sub>2</sub>O pressure below cabin, the diaphragm will open the demand valve.<ref name="aoh" /></blockquote>		<blockquote>When the pressure drops approximately 3-inch H<sub>2</sub>O pressure below cabin, the diaphragm will open the demand valve.<ref name="aoh" /></blockquote>

			<div style="clear:right; float:right; width:200px; margin:0.15em 0 0.6em 1.25em;">
			[[File:Apollo CM ECU left side small.jpg\|link=File:Apollo CM ECU left side full.jpg]]
			<div style="font-size:13px; line-height:1.35; margin-top:6px;">The same corner: demand regulator at the top, cabin return in the middle, coolant panel below. Photograph by Steve Jurvetson, 2020.</div>
			</div>
	A relief valve in the same assembly vents the suits if they rise to between 2 and 9 inches of water above the cabin. The flight report's table says the regulator supplies oxygen when the suit circuit is 3.0 inches of water, within 0.5 inch, below cabin pressure, and relieves when the suit is 2 inches of water above the cabin.<ref name="csm" /> The suits stay just under cabin pressure, so they do not balloon.		A relief valve in the same assembly vents the suits if they rise to between 2 and 9 inches of water above the cabin. The flight report's table says the regulator supplies oxygen when the suit circuit is 3.0 inches of water, within 0.5 inch, below cabin pressure, and relieves when the suit is 2 inches of water above the cabin.<ref name="csm" /> The suits stay just under cabin pressure, so they do not balloon.

Line 100:		Line 103:

	The flight report gives that suited case as 3.75 psia, within 0.25 psi, at flow rates up to 0.67 pound per minute.<ref name="csm" /> Before entry the crew closed the suit-circuit return valve, so the demand regulator, not the cabin, held suit pressure for the descent.<ref name="aoh" />		The flight report gives that suited case as 3.75 psia, within 0.25 psi, at flow rates up to 0.67 pound per minute.<ref name="csm" /> Before entry the crew closed the suit-circuit return valve, so the demand regulator, not the cabin, held suit pressure for the descent.<ref name="aoh" />

	~~<div style="clear:both; margin:1em auto 1.2em; max-width:280px; text-align:center;">~~
	~~[[File:Apollo CM ECU left side small.jpg\|link=File:Apollo CM ECU left side full.jpg]]~~
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">The same corner in a wider view: demand regulator at the top, cabin return inlet in the middle, coolant panel below. Photograph by Steve Jurvetson, 2020.</div>
	~~</div>~~

	While the cabin was sealed and the return valve was open, makeup for the suit loop could come from the cabin, and the cabin regulator made that up. The handbook says makeup comes from the demand regulator when the return valve is closed, and from the cabin when the return valve is open.<ref name="aoh" />		While the cabin was sealed and the return valve was open, makeup for the suit loop could come from the cabin, and the cabin regulator made that up. The handbook says makeup comes from the demand regulator when the return valve is closed, and from the cabin when the return valve is open.<ref name="aoh" />
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	Two compressors circulated the loop. One ran at a time. Gas from the suits came back through the return manifold, through a debris screen, through a compressor, through the lithium hydroxide, and back to the suits.<ref name="csm" />		Two compressors circulated the loop. One ran at a time. Gas from the suits came back through the return manifold, through a debris screen, through a compressor, through the lithium hydroxide, and back to the suits.<ref name="csm" />

	{\| style="margin:~~1em auto~~ 1.~~2em~~; border-collapse:separate; border-spacing:~~16px~~ 0;"		<div style="clear:both;"></div>
			{\| style="width:100%; margin:0.4em 0 1.3em; border-collapse:separate; border-spacing:14px 0;"
	\|- style="vertical-align:top;"		\|- style="vertical-align:top;"
	\| style="width:~~220px~~;" \| [[File:Apollo CM cabin return small.jpg\|link=File:Apollo CM cabin return full.jpg]]		\| style="width:33%; text-align:center;" \| [[File:Apollo CM cabin return small.jpg\|link=File:Apollo CM cabin return full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">Cabin return inlet and the suit-circuit return isolation valve. ~~With the cabin sealed, this connection is why suit pressure and cabin pressure stay together. Photograph from the spaceaholic~~ collection, 2010.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px; text-align:left;">Cabin return inlet and the suit-circuit return isolation valve. Spaceaholic collection, 2010.</div>
	\| style="width:~~220px~~;" \| [[File:Apollo CM suit return small.jpg\|link=File:Apollo CM suit return full.jpg]]		\| style="width:33%; text-align:center;" \| [[File:Apollo CM suit return small.jpg\|link=File:Apollo CM suit return full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">Suit oxygen return~~. Gas coming back from the suits passed~~ the debris~~-trap~~ screen ~~before the compressors and the lithium hydroxide~~. ~~Photograph from the spaceaholic~~ collection, 2010.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px; text-align:left;">Suit oxygen return, ahead of the debris screen. Spaceaholic collection, 2010.</div>
	\| style="width:~~240px~~;" \| [[File:Apollo CM suit compressors small.jpg\|link=File:Apollo CM suit compressors full.jpg]]		\| style="width:34%; text-align:center;" \| [[File:Apollo CM suit compressors small.jpg\|link=File:Apollo CM suit compressors full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">~~The two suit~~-circuit compressors, cover off. One ~~circulated the oxygen loop~~ at a time. ~~Photograph from the spaceaholic~~ collection, 2010.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px; text-align:left;">Suit-circuit compressors, cover off. One ran at a time. Spaceaholic collection, 2010.</div>
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	Two beds sat in parallel. Each was sized for 1.5 man-days. The crew changed them alternately, one every 12 hours, so the carbon dioxide did not jump when a fresh bed went in. An 8- to 10-day mission carried 20 beds. The holder could be opened without dumping the suit loop, including with the cabin already at vacuum. The carbon dioxide limit was 7.6 mmHg. Readings usually stayed near 3 mmHg.<ref name="csm" />		Two beds sat in parallel. Each was sized for 1.5 man-days. The crew changed them alternately, one every 12 hours, so the carbon dioxide did not jump when a fresh bed went in. An 8- to 10-day mission carried 20 beds. The holder could be opened without dumping the suit loop, including with the cabin already at vacuum. The carbon dioxide limit was 7.6 mmHg. Readings usually stayed near 3 mmHg.<ref name="csm" />

	{\| style="margin:~~1em~~ auto 1.2em; border-collapse:separate; border-spacing:~~18px~~ 0;"		{\| style="margin:0.6em auto 1.2em; border-collapse:separate; border-spacing:22px 0;"
	\|- style="vertical-align:top;"		\|- style="vertical-align:top;"
	\| style="width:~~220px~~;" \| [[File:Apollo CM LiOH canisters small.jpg\|link=File:Apollo CM LiOH canisters full.jpg]]		\| style="width:216px; text-align:center;" \| [[File:Apollo CM LiOH canisters small.jpg\|link=File:Apollo CM LiOH canisters full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">~~Lithium hydroxide canisters~~ A and B. The crew changed one at a time. Photograph by Steve Jurvetson, 2020.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px; text-align:left;">Canisters A and B. The crew changed one at a time. Photograph by Steve Jurvetson, 2020.</div>
	\| style="width:~~320px~~;" \| [[File:Apollo CM LiOH open small.jpg\|link=File:Apollo CM LiOH open full.jpg]]		\| style="width:349px; text-align:center;" \| [[File:Apollo CM LiOH open small.jpg\|link=File:Apollo CM LiOH open full.jpg]]
	<div style="font-size:13px; line-height:1.35; margin-top:6px;">One canister open. The round element is the lithium hydroxide and charcoal bed. ~~Photograph from the spaceaholic~~ collection, 2010.</div>		<div style="font-size:13px; line-height:1.35; margin-top:6px; text-align:left;">One canister open. The round element is the lithium hydroxide and charcoal bed. Spaceaholic collection, 2010.</div>
	\|}		\|}