Only if that exact model and size is approved for a vertical orientation. The USC Foundation approves each backflow assembly for specific orientations, and rotating it voids the approval. Arizona requires USC-approved assemblies installed to the manufacturer's specifications, so a vertical RPZ or double check needs a vertical-listed model, not a turned horizontal one.
Why orientation is part of the approval
The USC Foundation for Cross-Connection Control and Hydraulic Research tests backflow assemblies in the lab and in the field, then lists the ones that pass. The notice at the front of its list is blunt: "all of the assemblies listed are Approved for the INDICATED ORIENTATION(S) ONLY. Rotation of assemblies on either axis will invalidate the USC Foundation's Approval."
The reason is mechanical. Check valves, springs and an RPZ's relief valve were tested in one position. Gravity acts differently on the internal parts when the body is turned, and the relief valve has to sit where it can dump water and drain. So a model gets listed only for the positions it was tested in.
Arizona leans on that list. A.A.C. R18-4-215 says a required assembly with test cocks must have "been issued a certificate of approval" by the USC Foundation or another third-party certifier approved by ADEQ. The same rule says any required backflow prevention "shall be installed in accordance with the manufacturer's specifications." Phoenix's location guideline, TRT 00634, also calls for assemblies certified by the USC Foundation or another certifier ADEQ approves.
How to read the orientation codes
Each entry on the USC list shows an orientation code. The key on the list's orientation page uses H for horizontal, V for vertical, U for up and D for down:
| Code | What it means |
|---|---|
| H | Horizontal run, water flowing sideways |
| VU | Straight vertical, water flowing up |
| VD | Straight vertical, water flowing down |
| VUVD | Inlet flows up, outlet flows down (an "N" shape) |
| VUVU | Inlet flows up, outlet flows up |
| VDVU | Inlet flows down, outlet flows up |
| VUH | Inlet flows up, outlet runs horizontal |
So "vertical" isn't one thing. A model listed VU is approved for flow going up through a vertical body. It is not approved for flow going down unless VD is also listed for that size.
How common vertical approvals are
Horizontal is the norm, especially for RPZs. By our count of the October 1, 2026 PDF list, reduced pressure principle (RP) entries carry the H code far more than any other, and straight vertical-up RP listings are rare. Double check entries show many more VU listings. Most RPs that go vertical are purpose-built "N" or "Z" style bodies with a U-turn in the waterway.
A few examples from the same list show why you check the exact model:
- Watts LF009QT (a common domestic RPZ): listed H only.
- Watts LF909QT: H, and VU in the 3/4-inch and 1-inch sizes.
- Watts LF919QT, LF919AQT and LF919ZQT: VD, VUVD and VUVU in turn.
- Wilkins 975XL2: H only, while the 975XL2SE is listed VUVD and VUVU.
The USC Foundation's own example makes the same point. Its Excel list can be filtered for a lead-free, 2-inch RP with "Vertical up inlet and vertical down outlet," and the Foundation says that search "would generate a list of five acceptable assemblies." Five, out of a list that runs hundreds of pages.
Pressure vacuum breakers are their own case. Almost every PVB entry on the list is VUH, inlet coming up and outlet going sideways, so they're never laid flat or flipped. A PVB that isn't upright can also malfunction; see why a pressure vacuum breaker leaks from the top.
What Phoenix checks besides orientation
A vertical assembly still has to meet every placement rule. In Phoenix, under the 2024 IPC as amended by Ordinance G-7397:
- Clearance: "not less than 12 inches between the lowest portion of the assembly and grade, floor, or platform" (Section 608.15.3).
- Height: "Elevated installations that exceed 5 feet above the floor or grade shall be provided with a platform capable of supporting a tester or maintenance person."
- Working space: "A minimum 3-foot (914 mm) clear space shall be maintained for testing, maintenance, and repair."
- No pits: "Backflow prevention devices shall not be installed in pits, underground vaults, or submerged locations" (Section 608.8.1).
Tall vertical runs can push test cocks above 5 feet, which brings in the platform rule. In Mesa, point-of-use assemblies inside a building must be "installed no more than five (5) feet above finished floor level" (City Code 8-1-9).
Phoenix also requires a permit for "Installation, alteration or replacement of all backflow prevention assemblies," including internal ones, per TRT 00634. And under Phoenix's amended Section 312.11.2, assemblies "shall be tested at the time of installation, immediately after repairs or relocation and at least annually." Re-orienting or relocating an assembly means a new test.
How to get it right before you buy
- 1Measure the space first. Note whether the pipe runs up, down or sideways where the assembly will sit.
- 2Pick the model from the current USC list by type, size and orientation code, not from a catalog photo.
- 3Confirm it with your water provider. Mesa, for one, says its department may approve an alternative assembly only if it carries a USC or equivalent third-party approval (City Code 8-1-4).
- 4Plan the relief drain for an RPZ, since vertical bodies put the relief port in a different spot.
- 5Leave room for the tester and keep test cocks within reach, or plan a platform.
If an existing assembly was turned to fit and never matched its listing, the fix is usually a vertical-listed model or a re-pipe so the listed one sits right. HQ tests, repairs and replaces domestic backflow assemblies across the Valley and can check a model against its listing before anything is cut in.
For the full placement rules, read where an RPZ can be installed in Arizona. For the drain side, see why an RPZ needs an air gap drain, and for choosing between the two testable types, RPZ vs double check.