TECTULby IMR

Fluid conveyance · PVC foot valves

TECHNICAL DATA SHEET

FT-TC-VAL-PIE-PVC-001

Issue date: August 4, 2026 · Rev. 001

Check the current version

PVC-body foot valves (with and without air release)

TECTUL · Dispatch across Colombia · Exports to Central & South America

This sheet covers the two PVC-body foot valves in the TECTUL catalog: the PVC foot valve, from 3/4″ to 4″ and the most economical reference in the whole suction block, and the Tecno Plastic threaded PVC air-release and foot valve, from 1/2″ to 3″, which integrates an air release into the same body. PVC is not chosen for being cheaper: it is chosen because bronze does not withstand water with agricultural chemicals, dissolved fertilizers or brackish water, which is exactly the irrigation and intake service this valve lives in. In exchange, the material imposes two limits bronze does not have: the PVC-U maximum service temperature (60 °C, 140 °F) and the plastic thread's fragility against over-tightening. The suction physics —head loss, NPSH deduction, seat velocity and minimum submergence— is the same for the whole family and is applied here to this material.

SKU VT-59223 (PVC foot valve, 3/4″-4″, 8 published sizes) · PVC block of 2 references; the second is the Tecno Plastic threaded PVC air-release and foot valve (1/2″-3″, 6 sizes)

1. Technical specifications: the 2 PVC-body references

A foot valve is a check valve with an integral strainer installed at the submerged end of the suction line: it holds the water column when the pump stops —keeping the line primed— and stops coarse solids. In a PVC body, TECTUL publishes two references. This family has no international pressure-rating standard and neither manufacturer publishes a working pressure per size: the design quantity is head loss (section 4) and the material's hard limit is temperature (section 2). Where the manufacturer publishes no figure, this sheet states «confirmed on quotation».

1.1 PVC-body references in the TECTUL catalog

The PVC foot valve does not publish intermediate sizes other than those listed: the series is the one in the table, not a continuous series. Metal-body foot valves and suction checks (bronze, aluminum, brass, iron) are not in this sheet: they are in FT-TC-VAL-PIE-METAL-001.

1.2 When PVC and when metal

2. The material's limit: 60 °C and pressure loss with temperature

PVC-U is a thermoplastic: its mechanical strength falls continuously as temperature rises, not in a step. The industry publishes that fall as derating factors on the pressure declared at 23 °C, identical for pipe, fittings and valves of the same compound. Since these two foot valves publish no base pressure at 23 °C, the table gives no psi value: it gives the fraction of the material's capacity remaining at each temperature, and above all it sets the ceiling.

The same factor table published by the standard's manufacturers for PVC-U and consistent with the rule used across the rest of TECTUL's plastic catalog (FT-TC-ACC-PVCP-001 and FT-TC-VAL-PLAST-001, not repeated here). On a foot valve the figure carries a favorable nuance: it works submerged at the suction end, where pressure is low by definition, so the critical restriction is usually not pressure but the water temperature and that of the thread above the level. The seal elastomer imposes its own ceiling (EPDM is around 100 °C and NBR lower): the lower of the two always governs, and on this valve that lower one is the PVC body at 60 °C.

What PVC does and does not solve

It does solve: corrosion. In fertigation, in chloride-bearing intakes and in brackish water, the bronze or brass body is attacked by dezincification and pitting, and the wear is invisible until the seat stops sealing and the pump loses prime. PVC-U has no such failure mechanism, which is why it is the correct —not the cheap— option in that service.

It does not solve: impact. PVC-U is rigid and brittle compared with bronze: it withstands impact poorly, as well as dragging against the cistern bottom and the weight of a poorly supported pipe hanging from its thread. Nor does it solve temperature, or prolonged ultraviolet exposure if the valve ends up out of the water at the tank's low level.

3. Plastic thread, over-tightening and the integral air release

3.1 The plastic thread seals like the metal one, but fails differently

The 60° tapered thread for thermoplastics (ASTM F1498) seals by wedging interference, just like metal NPT. The difference is the modulus of elasticity: PVC-U is orders of magnitude less rigid than steel or bronze, so the same wrench that merely tightens a metal nipple opens the body of a PVC valve. Over-tightening is the number-one cause of plastic thread failure, and on a foot valve the symptom is twofold: a leak that breaks the prime, and ovalization of the body that prevents the poppet disc from seating. The crack usually appears hours or days after installation, not during it.

3.2 What the integral air release does and when it pays for itself

The block's second reference incorporates an air release (air valve) in the same foot valve body. Its function is to evacuate the air trapped in the suction column when priming the pump, and to evacuate it again each time the line fills after a stop.

The problem it solves: when starting a pump on an empty or partly empty pipe, the column's air does not leave by itself. It stays compressed at the high points and forms an air lock: the pump turns, takes no water, runs dry and can damage the mechanical seal. With the air release, that air has a way out while the water rises, and the column fills completely. When the water reaches the air release, the float or closing element seals it and the valve keeps working as an ordinary foot check.

When it justifies the extra cost over the plain PVC foot valve (about 2.7 times costlier): on long suction lines, with irregular routing or high points, in installations that start and stop frequently, and in irrigation systems where manual priming with a bucket is impractical. On a short, straight suction from a cistern, the plain PVC foot valve does the job.

4. Suction physics applied to the PVC body

4.1 The design quantity is head loss, not pressure

As in the metal block, the PVC foot valve is sized by what it takes away from the suction, not by what it withstands. The poppet disc —the type on both of these references— has an equivalent length of L/D = 420 pipe diameters per the Crane Technical Paper No. 410 table; the hinged or swing-disc check has L/D = 75, nearly six times less. As a field figure, a manufacturer's sizing guide reports that at 2 m/s at the seat, the poppet-type foot valve generates between 0.3 and 0.6 bar (3 to 6 meters of water column) of loss.

4.2 Worked example: how much NPSH the valve takes

The exercise does not replace the calculation of the actual system —which requires the specific pump's required-NPSH curve and the exact line losses— but it sets the magnitude: the foot valve alone consumes almost half of the suction margin in this case. If the reservoir sits at higher altitude above sea level, Ha drops and the margin narrows further: on the Colombian high plateau that term is no longer 10.33 m and must be corrected for altitude before concluding anything.

4.3 Choose by seat velocity, not by pipe diameter

The most common selection error is ordering the foot valve in the same size as the pipe. The correct rule is the flow velocity through the seat: 0.5 to 1.0 m/s. Below that, the poppet disc may not seat with enough force and the valve drips at shutdown; above it, loss rises fast and eats the NPSH. The strainer must also have between 3 and 5 times the pipe cross-sectional area so that it is not itself the dominant restriction. It is normal and correct for the valve to end up one size above the line: the PVC series in this sheet publishes 8 sizes precisely to allow that.

4.4 Minimum submergence and mounting

Minimum submergence ≥ 2 times the valve's nominal diameter, measured from the minimum water level to the valve inlet. With less, the suction forms a surface vortex that draws air: loss of prime, noise, vibration and intermittent cavitation. On the other side, the valve must not rest on the reservoir bottom: it needs clearance so that water enters through the full strainer area and so that it does not draw up settled sediment. In larger suction structures (sumps, high-flow pumping wells) the industry criterion is ANSI/HI 9.8, Rotodynamic Pumps for Pump Intake Design, which incorporates approach velocity and the Froude number.

The poppet disc closes by gravity: the valve is installed vertical or with a maximum tilt of 45° from vertical. Horizontally, closing is not reliable unless the manufacturer confirms an assist spring. The suction line must rise on a continuous slope toward the pump, with no high points to trap air — and if the routing forces them, that is exactly the installation that justifies the air-release reference from section 3.

5. Frequently asked questions

How many psi does a PVC foot valve withstand?

Neither manufacturer in this sheet publishes a working pressure per size, and this family has no international pressure-rating standard. That is consistent with the function: the valve works submerged at the suction end, where pressure is low and what governs design is head loss. What is a firm material limit is temperature: 60 °C (140 °F). If the specification requires a declared pressure value, it is confirmed on quotation per reference and lot.

PVC or bronze foot valve?

PVC when the fluid corrodes metal: irrigation with dissolved fertilizers, brackish water, chloride-bearing wells, water with dosing chemicals. Bronze when the service is clean fresh water, permanent and mechanically demanding, because the metal seat lasts longer and the body better tolerates impact and tightening. Cost should not be the criterion: the PVC foot valve is the catalog's cheapest reference, but it is specified by chemistry.

What is the air release on the Tecno Plastic reference for?

It evacuates the air trapped in the suction column when priming the pump and each time the line refills after a stop. Without it, that air stays compressed at the high points and forms an air lock: the pump turns, takes no water and runs dry. It is justified on long or irregularly routed suction lines and in installations that start and stop frequently. On a short, straight suction, the plain PVC foot valve is enough.

How hard do I tighten a PVC foot valve?

Hand-tight to the stop, plus 1 or 2 turns with a wrench, with PTFE tape or a PVC-compatible sealant. No more. Over-tightening is the number-one cause of plastic thread failure and on a foot valve it produces two failures at once: a leak that breaks the prime and ovalization of the body that prevents the disc from seating. In a transition to metal, the plastic male always goes inside the metal female, never the reverse. And always wrench on the body, never on the strainer.

Does it work for hot water or a warm process?

Not above 60 °C (140 °F): that is the PVC-U ceiling and above it the valve does not apply, no matter how low the pressure. For threads in continuous service the practical limit drops to 43 °C (110 °F). Above those values a metal body applies (FT-TC-VAL-PIE-METAL-001).

How deep should the valve sit?

With minimum submergence of at least 2 times its nominal diameter from the minimum water level, and without resting on the bottom. With less submergence the suction forms a surface vortex and draws air, causing loss of prime and intermittent cavitation; resting on the bottom it draws up sediment and clogs the strainer quickly.

6. Application notes

7. Technical notice and limitation of liability