Can a Backflow Preventer cCause Low Water Pressure In My Building?

Backflow preventers create a deliberate restriction in your plumbing to keep contaminated water from reversing into your potable supply. That restriction introduces a measurable pressure drop, and if the device is undersized, clogged, worn, or misinstalled, your building can experience noticeable low water pressure and reduced flow.

In this guide, Atlas Backflow Services breaks down the why, how to diagnose it, and the fixes—plus when to schedule professional Backflow Testing Los Angeles to stay compliant and comfortable.

How backflow preventers affect pressure (by design)

All backflow assemblies impose “head loss” (pressure drop) as water passes through. Typical ranges:

• DCVA (Double Check Valve Assembly): Modest loss at low flows, increasing at higher flows. It’s common to see a few PSI drop at light demand and 7–12 PSI at peak usage.

• RP (Reduced Pressure) Assembly / RPZ: Higher inherent loss due to the relief/zone design. Often 10–15+ PSI at common building flows.

• PVB (Pressure Vacuum Breaker): Generally lower drop than an RP, more than a simple check.

Two important points:

• Static pressure (what a gauge reads with no water running) might look fine, but dynamic pressure (while fixtures are flowing) is what you feel in showers and hose bibs. Backflow devices primarily affect dynamic pressure/flow.

• Manufacturers publish flow vs. loss curves. If the device is sized too small relative to peak GPM, you’ll feel it.

When a backflow preventer is the culprit

Beyond the inherent loss, several issues can make a backflow device cause abnormally low pressure:

1. Debris lodged in check valves

   • Construction sediment, scale, or sand can stick to the check seats and restrict passage.

   • Signs: Pressure was fine, then dropped after a main break, construction, or seasonal irrigation startup.

   • Fix: Disassemble/clean checks, flush lines, and consider upstream strainers where allowed.

2. Worn internal parts (rubber discs, o‑rings, springs)

   • Aging components don’t seal or move properly, increasing resistance.

   • Signs: Growing pressure complaints over months, older device (5–10+ years) without maintenance.

   • Fix: Rebuild with the manufacturer kit and re-test.

3. Undersized device for your peak flow

   • If the assembly size was matched to the pipe, not the demand, expect high losses at peak hours.

   • Signs: Pressure is OK at light use, drops sharply during showers, laundry, or irrigation.

   • Fix: Replace with a properly sized model or install parallel assemblies (where code allows) to split flow.

4. Partially closed shut-off valves or test cocks

   • Handle looks “open,” but the ball or gate isn’t fully open—or a test cock is left cracked after a previous test.

   • Signs: Sudden pressure drop after service or testing.

   • Fix: Verify all valves fully open; correct orientations for quarter-turn handles.

5. Clogged strainers upstream

   • Strainers protect the device but need maintenance. A loaded screen throttles flow.

   • Fix: Clean or replace screens, then re-test.

6. Relief valve weeping on an RPZ

   • A relief valve that’s partially open spills water and reduces available downstream pressure.

   • Causes: Debris on the first/second check, high/variable supply pressure, thermal expansion, or failing relief internals.

   • Fix: Diagnose with gauges, repair/rebuild, and address pressure control (PRV/expansion tank).

7. Improper installation

   • Excess elbows, wrong orientation, no clearance, buried or confined installs, or long undersized runs before/after the assembly.

   • Fix: Re-pipe to manufacturer and code recommendations for straight lengths and access.

If any of these sound familiar, it’s time for Backflow Testing Los Angeles with Atlas Backflow Services. We’ll measure actual differential pressures, isolate the cause, and get you back to normal.

When it’s not the backflow preventer

Low pressure often has multiple contributors. Before blaming the assembly alone, consider:

• PRV (Pressure Reducing Valve) issues: Many Los Angeles buildings have a PRV to tame high city pressure. A failing or misadjusted PRV causes low flow and pressure.

• Thermal expansion in closed systems: Without a healthy expansion tank, spikes can stress checks and PRVs, leading to erratic pressure and nuisance relief events.

• Meter or service line limitations: An undersized or fouled water meter, or an aging service line with internal buildup, can starve the building.

• Fixture restrictions: Clogged aerators, whole-house filters, or water softeners can be the real choke point.

• Municipal variations: LADWP pressure can vary by zone and elevation. High hillside areas experience more pronounced drops at peak demand.

A professional approach tests upstream and downstream of the backflow assembly to separate device-related loss from system-wide limitations.

Simple diagnostics you can do safely

• Check static vs. dynamic pressure: Put a gauge on a hose bib near the backflow. Note pressure at rest, then while multiple fixtures run. A large drop indicates flow restriction somewhere.

• Look and listen at the assembly:

  • Is an RP relief port dribbling or dumping water?

  • Are shutoffs fully aligned with flow?

  • Any obvious kinks or undersized hoses attached downstream?

• Timing matters: Does pressure tank at specific times (morning showers, irrigation cycles)? That points to undersizing or distribution bottlenecks.

• Recent changes: New landscaping, filters, or tenants? Increased demand can expose marginal sizing.

If you’re unsure, schedule Backflow Testing Los Angeles. Atlas Backflow Services will perform certified testing, log differential readings, and provide a clear, actionable report.

How we fix low pressure linked to backflow devices

Atlas Backflow Services follows a code-first, data-driven process:

• Certified testing and diagnosis

  • Verify first and second check performance and relief opening points (for RPZ).

  • Measure pressure drop across the device at representative flows.

• Targeted maintenance or rebuild

  • Clean checks and seats, replace rubber kits and springs, and service shutoffs and test cocks.

  • Clean strainers and flush debris.

• Right-size the solution

  • Recommend a correctly sized device based on peak GPM and manufacturer loss curves.

  • Where allowed, install parallel assemblies to reduce head loss and add redundancy for commercial buildings.

• Pressure management

  • Adjust or replace the PRV.

  • Install/charge an expansion tank to stabilize downstream pressure and protect checks.

  • Add water hammer arrestors if quick-closing valves are present.

• Piping and layout improvements

  • Correct orientation, provide straight runs, and eliminate unnecessary restrictions.

  • Ensure a proper, air-gapped drain for RPZs without creating backpressure.

After repairs or replacement, we complete Backflow Testing Los Angeles, file compliance documents with your water purveyor, and set reminders so you never miss annual certification.

Los Angeles specifics you should know

• Annual testing is required by most LA-area purveyors. Skipping testing allows small issues (like debris on a check) to evolve into big pressure problems—or compliance violations.

• High static city pressure is common, but that doesn’t guarantee good flow. A tuned PRV and a healthy, properly sized backflow preventer are key to stable performance.

• Irrigation and fire lines have their own devices. Cross-connections or incorrectly shared supply lines can starve domestic fixtures during peak irrigation or testing.

Atlas Backflow Services specializes in Backflow Testing Los Angeles and understands local codes, LADWP requirements, and the unique pressure profiles across LA neighborhoods.

Final takeaway

• Yes, a backflow preventer can cause low water pressure—either because of its inherent pressure drop or due to faults like debris, wear, undersizing, or installation issues.

• The fix usually isn’t guesswork. Certified testing and proper sizing quickly reveal whether the device is at fault or if the issue lives with the PRV, meter, filters, or distribution piping.

• Most problems resolve with cleaning, rebuilding, or right-sizing the assembly and tuning your pressure controls.

If your building is experiencing low water pressure, don’t chase symptoms. Contact Atlas Backflow Services for expert Backflow Testing Los Angeles. We’ll diagnose the cause, restore strong and steady flow, and keep your property compliant—without wasting time, water, or money.