From trap seal to trigger
What does a trap primer do for a floor drain?
A trap primer adds water to the trap below a floor drain so that the water seal stays in place. Jay R. Smith’s range page defines it as a flow control valve that adds water to a P-trap to maintain a water seal. It is separate from the grate and drain body seen at the floor.
The Wisconsin Department of Health Services says sewer gas can enter a home through a floor drain. Its advice is to flush floor and sink drains with water so the traps do not dry out. A primer does that topping-up automatically.
| Term | What it means |
|---|---|
| Trap primer | A valve that adds water to a trap to maintain its seal. |
| Pressure-drop primer | A primer that releases water when supply-line pressure drops. |
| Electronic primer | A primer that opens a solenoid valve on a timer. |
| Distribution unit | A fitting that divides one primer’s water among traps. |
| Make-up line | The pipe from the primer to the trap. |
How does a pressure-triggered primer work?
A pressure-triggered primer releases water when use of a fixture on the same line drops the line pressure by the amount that model needs. The sequence combines makers’ descriptions and is not a record of any product.
- The primer sits on a cold water line serving a fixture in frequent use.
- Someone opens a valve or faucet on that line.
- Water flows and the pressure in the line drops.
- The primer releases water.
- The water runs down the make-up line to the trap.
- The water seal is topped up.
Zurn’s Z1022-XL sheet says a piston inside the primer rises when water flows through the supply line. MIFAB says its M-500 is activated automatically when a valve or faucet on the line is opened. A timed primer is also connected to a water line, but a timer takes the place of steps 2 and 3.
Pressure-triggered or timed: what is the difference?
The difference is what makes the primer release water: use of a nearby fixture, or a clock.
| Question | Pressure-triggered | Timed |
|---|---|---|
| What opens it? | A pressure drop when a fixture on the line is used | A timer that opens a solenoid valve |
| Depends on fixture use? | Zurn: install in a frequently used line | MIFAB: MI-100 can be located anywhere in the water supply |
| Adjustment? | MIFAB: the M-500 requires no adjustments | Sioux Chief: frequency and duration adjustable on the 695-ES01 |
| Power? | None named in the sheets read | Sioux Chief: 120V AC supply |
Jay R. Smith describes its electronic primers as giving a timed injection of water to floor-drain P-traps.
What figures do makers publish for named primers?
Each maker publishes its own figures, and they differ from model to model.
| Model | Trigger | Maker’s figure |
|---|---|---|
| Watts LFTP300-DR | Pressure drop | 10 psi drop; 25 to 125 psi operating pressure |
| Zurn Z1022-XL | Pressure drop | 2 to 3 psi drop at 20 to 80 psi static; 0.5 GPM minimum flow |
| Precision Plumbing Products (PPP) P1-500 and P2-500 | Pressure drop | Fixture drop of at least 10 PSIG; effective range 20 to 80 PSIG |
| Jay R. Smith Trap-Defender | Pressure drop | As little as a 3 PSI drop |
| MIFAB MI-100 | Timer | At least 2 ounces to every port over 24 hours |
| Sioux Chief 695-ES01 | Timer | 2 ounces daily as factory-set |
| PPP Prime Time PT-4 to 2130 | Timer | 6 seconds once every 24 hours as preset |
So do drain counts. MIFAB’s page title for the M-500 says up to 6 drains, and MIFAB gives 1 to 30 traps for the MI-100. Zurn’s product page offers 2, 3 and 4-outlet distribution units. Sioux Chief says primers without an access box can prime up to 8 drains with 695-series accessories, and that the design engineer or installing contractor should determine capacity.
Which standards cover trap primers?
ASSE International’s product standards list describes three standards for keeping a trap seal, each for a different device:
ASSE 1018-2023
Primer valves supplied with potable water; a means of preventing backsiphonage shall be part of the device. Watts states the LFTP300-DR is tested and approved in conformance with ASSE Standard 1018; it names no edition.
ASSE 1044-2023
Primers fed from a fixture drain line, a fill valve or a flushometer valve tailpiece, and electric trap seal primers. Sioux Chief’s specification sheet for the 695-ES01 says the trap primer shall be listed and certified to ASSE 1044; it names no edition.
ASSE 1072-2025e1
Barrier type devices that help protect the seal by minimizing evaporation, on floor drains that comply with ASME A112.6.3.
ASSE 1010
A different function: Sioux Chief fits an ASSE 1010 water hammer arrester to protect the solenoid.
- Record the standard and edition the maker names
- Check which device type that standard covers
- Note the maker’s wording: tested, listed or certified
- Ask for the certifier’s listing entry
- Ask which edition the adopted code names
What services and access does each type need?
Both types need a water connection and access; the two timed units whose instructions were read, Sioux Chief’s and PPP’s, also need mains power. Makers’ instructions show what to coordinate:
Water connection
PPP puts the P1-500 and P2-500 on a cold fresh water line of 1 1/2 in diameter or less, near a fixture that creates the pressure drop.
Mounting height
Zurn asks for the Z1022-XL to sit at least 12 in above the grid of the floor drain. For the P1-500 and P2-500, PPP asks for at least 12 in above the finished floor, and says to allow 1 ft of elevation for every 20 ft of make-up line.
Power
Sioux Chief’s 695-ES01 connects to a 120V AC supply. PPP requires the Prime Time’s three-wire connection to follow local and national electrical codes.
Backflow protection
Watts lists an integral air gap on the LFTP300-DR.
For checking, Zurn says a periodic look through the air gap vacuum ports, or at the drain trap, confirms operation. MIFAB’s M-500 has four view holes; PPP’s Prime Time has a Test button.
Is a trap primer required?
That depends on the plumbing code adopted where the project is built. Two state rules read for this guide:
| Source | What it says |
|---|---|
| Wisconsin SPS 382.32 | Paragraph (3)(c), on loss of trap seal, names a trap seal primer valve, or other protection acceptable to the department, for traps subject to evaporation. The text retrieved was incomplete; read the section in full with the local authority. |
| Wisconsin, note to the rule | Lists mineral oil, vegetable oil, propylene glycol and glycerin as liquids acceptable for reducing evaporation. |
| Wisconsin, barrier devices | Shall conform to ASSE 1072. |
| Minnesota Rules 4714.1007 | Deletes UPC section 1007 in full; that section’s text was not read for this guide. |
| Model codes (IPC, UPC) | Text not retrieved for this guide; confirm with the local authority. |
How should a buyer assign trap-primer scope?
Give the primer its own line on the schedule. These steps are procurement guidance, not a plumbing design.
- List the drains. Mark those that will rarely receive water.
- Ask the local authority. Is seal protection required, and by which means?
- Choose the trigger. Pressure drop beside a fixture in regular use, or a timer.
- Check the services. Cold water line, power for a timed unit, mounting height.
- Settle the distribution. Use the chosen model’s own drain count.
- Record the standard. ASSE 1018 or 1044, in the maker’s words.
- Name the parties. Who supplies drain, trap, primer, piping and power.
Do not copy settings between projects
A pressure drop, interval, volume or drain count from one primer does not set the design for another model or building. Use the chosen device’s documents.
What should you send and ask before a quotation?
A drain quotation may cover only the grate and body. These questions keep the primer from being left unassigned.
| Question | Why it matters |
|---|---|
| Does the quote include a primer? | The primer is separate from the drain. |
| What triggers it? | The two types need different services. |
| Which model and data sheet? | Figures and drain counts are model-specific. |
| Which standard, in what words? | ASSE 1018 and ASSE 1044 cover different devices. |
| Who provides water and power? | The Sioux Chief and PPP timed units need an electrical connection. |
| How is it inspected? | Some models have view ports or a test button. |
Include with your request
- Project location and adopted plumbing code
- Drains that will rarely be used
- Who designs the plumbing
- Primer type preferred, if any
- Drain model, outlet and quantity
Ask WNS Global to confirm in writing what a floor-drain quotation covers. This guide does not state that WNS Global supplies trap primers or primer connections, or that its products have the features, ratings or listings named above.
