Sump Pump Check Valve Size Chart: 1-1/4 vs 1-1/2 Inch

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Quick answer from a licensed plumber: Match the check valve to your discharge pipe, and never go smaller than the pump outlet. Every Zoeller, Wayne and Liberty submersible sump pump in the table below has a 1-1/2-inch discharge, and Zoeller and Liberty both say not to reduce it. Measure the pipe: 1-1/2-inch PVC is 1.900 inches across, 1-1/4-inch is 1.660. Not sure? A dual-size valve like the Zoeller 30-0181 fits either.

Pipe could be 1-1/4 or 1-1/2? Zoeller’s 30-0181 fits both. See the Zoeller 30-0181 on Amazon

What Size Is Your Pump’s Discharge?

Start at the pump, not the pipe. These are the discharge sizes Zoeller, Wayne and Liberty print for their residential sump pumps:

Maker	Models	Discharge (maker’s spec)
Zoeller	M53, M57, M63, M73, M98	1-1/2″ NPT
Wayne	CDU790, CDU800, CDU980E, CDU1000, SPF33, SPF50, WST30, CDT50	1-1/2″ NPT
Wayne	PTU33 pedestal pump	1-1/4″ NPT female thread
Liberty	230-, 250-, 280- and 290-Series	1-1/2″

Every submersible model on that list has a 1-1/2-inch outlet. Zoeller and Liberty are clear that the discharge must not be reduced below that. Zoeller: “DO NOT use a discharge pipe smaller than the pump discharge.” Liberty: “Do not reduce the discharge to below that which is provided on the pump,” and its warranty does not apply “if the pump discharge has been reduced in size.”

1-1/4 or 1-1/2: Measure the Pipe

The nominal size is not the outside of the pipe. Charlotte Pipe’s Schedule 40 PVC table gives the average outside diameters (Schedule 80 shares the same outside diameter; see Schedule 40 vs 80 PVC):

Nominal PVC size	Average outside diameter (Charlotte Pipe)	Distance around the pipe (our arithmetic)
1-1/4″	1.660″	about 5-1/4″
1-1/2″	1.900″	about 6″
2″	2.375″	about 7-1/2″

Wrap a strip of paper once around the pipe, mark it, and measure the strip. About 5-1/4 inches is 1-1/4-inch pipe; about 6 inches is 1-1/2-inch. Most PVC is also printed with its size along the side.

Check Valves by Size and Connection

A check valve has to match the pipe size and the way it connects: a rubber coupling that clamps over the pipe, a glued (solvent-weld) joint, or male threads that screw into the pump.

Valve	Fits	Connection	Maker notes
Zoeller 30-0181	1-1/4″ or 1-1/2″	Rubber couplings or solvent weld	“Can be used with 1-1/4″ or 1-1/2″ discharge piping”; connects to SCH40 PVC
Zoeller 30-0238	1-1/2″	Threads into the pump discharge; rubber coupling on top	“pre-drilled weep hole”; low-clearance pits
Zoeller 30-0040 (quiet)	1-1/2″	Solvent weld with unions	Spring-loaded flapper; “Rated for 50 PSI (115’ of head)”
Liberty CV2N1	1-1/4″ or 1-1/2″	Rubber slip connection with hose clamps	“CV2N1 combination 1-1/4″ or 1-1/2″”
Liberty QCV150 (quiet)	1-1/2″	Socket weld with threaded union	“Angled seat reduces ‘water hammer’ effect”
Superior Pump 99502	1-1/4″ or 1-1/2″	Rubber coupling	“4.3 PSI @ 140° F”; “Not for use with compressed air, gasses or potable water”
Superior Pump 99507 / 99509	1-1/4″ MPT / 1-1/2″ MPT	Male thread into the pump; 1-1/4″ barb or 1-1/2″ spigot on top	Superior lists both as ABS swing check valves. On a 1-1/2″ line, use the 1-1/2″ spigot end, not the barb

If you cannot tell which size you have, a dual-size valve such as the Zoeller 30-0181 fits either, and Zoeller says it can be spliced into an existing line easily.

Weep Hole or Not: It Depends on the Pump

Zoeller: “If a check valve is incorporated in the installation, a vent hole (approx. 3/16″ [5 mm]) must be drilled in the discharge pipe below the check valve and pit cover to purge the unit of trapped air.” The 53, 57 and 98 Series have a vent in the housing, but Zoeller says “an additional vent hole is recommended.” The 30-0238 inline valve comes with a pre-drilled weep hole.
Wayne: the CDU790, CDU800, CDU980E, CDU1000, SPF33, SPF50, WST30 and CDT50 pages each say “No need for weep holes; Unique Top Suction Design reduces clogging and prevents air lock condition.”
Liberty: its 250-, 280- and 290-Series pumps “come equipped with an air bleed hole in the base of the pump to help prevent airlock.”

More on why the hole matters in our sump pump weep hole guide.

I send an occasional note when a new guide goes up — repairs worth doing yourself, and the parts that actually last. No spam, no course funnel; written by a licensed Georgia plumber.

Where the Valve Goes

Required, not optional. Wayne: “IT IS REQUIRED TO USE A CHECK VALVE with this pump.” Liberty: “A check valve is required to prevent the backflow of liquid after each pumping cycle.” Zoeller: “DO install a check valve and a union in the discharge line.”
Easy to reach. Wayne says its check valve “may be positioned just above the basin to allow easy removal of the pump for cleaning and service.” Liberty adds that “A gate valve should follow the check valve to allow periodic cleaning of the check valve or removal of the pump.”
Arrow pointing away from the pump. For a pump that runs without moving water, Wayne lists a check valve “stuck closed or installed backwards” and Liberty one “stuck closed or installed backward.”

For quiet versus standard valves and the short-cycling and banging symptoms of a failed valve, see our sump pump check valve guide. A check valve also adds friction head, which our sump pump size calculator counts.

Before you cut into the discharge line: unplug the pump. Zoeller: “FOR YOUR PROTECTION, ALWAYS DISCONNECT PUMP FROM ITS POWER SOURCE BEFORE HANDLING.” Do not test PVC discharge pipe with compressed air: Charlotte Pipe warns that “Testing with or use of compressed air or gas in ABS / CPVC / PVC pipe or fittings can result in explosive failures.” Stop and call a licensed electrician or a licensed plumber if the pump is hard-wired with no plug, if the outlet has no ground or GFCI protection, or if there is water on the floor around the pump or the electrical panel.

Check Valves in Stock on Amazon

Each was new and in stock, shipped or sold by Amazon, when we checked on September 24, 2026. The Liberty CV2N1C and QCV150 listings we found were from outside sellers with low stock, so they are not linked:

Either size, slips over the pipe: Zoeller 30-0181 check valve, shipped and sold by Amazon.
1-1/2″, threads into the pump (Zoeller): Zoeller 30-0238 inline check valve (not linked: third-party seller only on 10/3/2026).
1-1/2″ quiet, glue-in with unions: Zoeller 30-0040 quiet check valve, shipped by Amazon.
1-1/2″ MPT, threads into the pump (Superior): Superior Pump 99509 check valve. We are not linking it right now: when we checked on September 29, 2026, the listing was down to its last unit from a third-party seller.
1-1/4″ MPT, for a 1-1/4-inch threaded outlet: Superior Pump 99507 check valve, shipped and sold by Amazon.

FAQ

What size check valve do I need for a sump pump?

The same size as the pump discharge and the pipe, never smaller. The Zoeller, Wayne and Liberty submersible sump pumps we looked up all have a 1-1/2-inch discharge, and Zoeller and Liberty both say not to reduce it. If you cannot tell whether your pipe is 1-1/4 or 1-1/2 inch, a dual-size valve such as the Zoeller 30-0181 fits either.

How do I tell 1-1/4 from 1-1/2 inch PVC?

Measure the outside. Charlotte Pipe lists Schedule 40 PVC at 1.660 inches outside diameter for 1-1/4 inch and 1.900 inches for 1-1/2 inch. A strip of paper wrapped once around measures about 5-1/4 inches on 1-1/4-inch pipe and about 6 inches on 1-1/2-inch pipe.

Can I use a 1-1/4 check valve on a 1-1/2 sump pump?

No. Zoeller says not to use a discharge pipe smaller than the pump discharge, Liberty says not to reduce the discharge, and Liberty’s warranty does not apply if the pump discharge has been reduced in size.

Do I need a weep hole with a sump pump check valve?

It depends on the pump. Zoeller says a 3/16-inch vent hole must be drilled below the check valve. Wayne says its top-suction pumps need no weep hole, and Liberty says its pumps have an air bleed hole in the base.

Where should a sump pump check valve go?

In the discharge line above the pump, where you can reach it. Wayne says its check valve may be placed just above the basin for easy pump removal, and Liberty recommends a gate valve after the check valve.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. Every part number, size, setting and fit on this page comes from the manufacturer pages and documents listed below, which we opened and read; product details come from those makers and from the Amazon listings, not from hands-on testing. Each linked product was shipped or sold by Amazon, new and in stock, when we checked on September 24, 2026. Where a link goes to Amazon we may earn a commission at no extra cost to you. Nobody pays to be included here. More on who writes this and how we pick.

Sources

Bottom Line

Size the check valve to the pipe, and the pipe to the pump: 1-1/2 inches on every submersible Zoeller, Wayne and Liberty model we looked up. Measure the pipe if you are unsure, or use a dual-size valve. Then follow your pump maker on the weep hole: Zoeller wants one, Wayne and Liberty build the air relief into the pump.

Sump Pump Check Valve Size: 1-1/4 vs 1-1/2 Inch