How High Should a Fertilizer Suction Tube Sit Above the Tank Bottom?
A suction tube should never rest on the tank floor. This guide sets the pickup height from four measurements, compares intake assemblies and gives a short commissioning test.
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A practical clearance, sediment and commissioning guide for fertigation intake assemblies
The suction tube should not lie on the bottom of a fertilizer stock tank. The reason is simple: undissolved fertilizer, precipitate and tank debris settle at the lowest point, so a bottom-resting intake can send that material into the injector, pump, filter or drip network. Extension guidance commonly describes a clearance of roughly 2 to 3 inches, 2 to 4 inches, or about 8 to 12 inches depending on the system and the amount of settled material. Those figures are reference points, not a universal installation dimension.
This guide owns the intake-clearance decision: how to set the pickup height from the sediment layer and the lowest operating level, how to choose between a bare tube, strainer, foot valve or suction assembly, and how to verify the arrangement under real draw conditions.
The clearance is a risk-control dimension, not a magic number
| Reference point | What it controls | Why the number changes |
|---|---|---|
| Tank bottom | Keeps the intake away from the first layer of settled solids | A flat tank, cone-bottom tank, sump and IBC outlet do not create the same sediment pattern |
| Top of the sediment layer | Prevents the intake from drawing material that has already settled | The layer depends on fertilizer solubility, water quality, mixing, hold time and prior cleaning |
| Lowest operating liquid level | Keeps the strainer submerged and prevents air ingestion during the final draw | A tube that is safe at full tank can vortex or uncover when the tank is nearly empty |
| Tank wall and nearby fittings | Avoids a local dead zone, wall contact or turbulence from an inlet | The intake may need lateral clearance as well as bottom clearance |
A useful specification is therefore not "install the tube 3 inches above the bottom." It is: keep the intake above the observed sediment layer, submerged at the lowest operating level, clear of walls and turbulence, and accessible for inspection. The fixed dimension can then be recorded on the drawing once the tank, formulation and operating level are known.
What the current guidance actually supports
University of Arkansas guidance places the intake strainer and suction tube about 2 to 3 inches above the bottom of the stock tank to avoid siphoning undissolved salts. University of Georgia guidance gives 2 to 4 inches and adds that the strainer should be inspected for clogging or cracks. Mississippi State guidance uses a much larger reference of about one foot when the objective is to avoid undissolved solids in a field fertilizer tank.
The difference is not an error to average away. It reflects different tank sizes, formulations, sediment risk and operating practices. Georgia guidance also recommends regular cleaning of the suction strainer, clean-water injection after use and periodic stock-tank cleaning, which makes the intake a maintenance component rather than a piece of tubing that can be installed once and forgotten.
Set the pickup height from four measurements
| Measure | How to obtain it | Decision use |
|---|---|---|
| S — settled layer | Measure the deepest settled sediment or sludge layer after the solution has stood for the normal hold time | The intake screen must remain above S with a practical inspection margin |
| Lmin — lowest operating level | Record the lowest liquid level at which the injector or pump is allowed to operate | The intake must remain submerged at Lmin without drawing a surface vortex |
| C — clearance from disturbances | Measure the clearance from the tank wall, inlet jet, agitator discharge or recirculation return | Move the intake away from local turbulence and wall-bound deposits |
| D — assembly dimensions | Confirm the suction-tube, strainer or foot-valve dimensions and the pump's allowable suction conditions | The assembly must not become the flow restriction or exceed the pump's suction limit |
For a simple tank, the drawing can show a minimum bottom clearance B that is greater than the measured sediment layer S plus the chosen margin M. The margin should be large enough to cover normal variation between batches, but not so large that the intake uncovers at Lmin. If those requirements conflict, change the tank operating volume, clean the tank more often, use a different pickup arrangement, or reconsider the concentration and mixing method. Do not solve the conflict by placing the strainer on the floor.
Choose the intake assembly by the failure you need to prevent
| Assembly | Useful when | Questions that still need an answer |
|---|---|---|
| Plain suction tube | The stock solution is clean, fully dissolved and already protected by upstream screening or a controlled mixing process | How is the tube held at the specified height? What prevents it from sliding to the bottom? |
| Tube with suction strainer | Small particles or undissolved residue are possible and the operator can inspect and clean the screen | Screen area, opening size, cleaning access and compatibility with the fertilizer concentrate |
| Foot valve with strainer | The pump needs a primed suction path or backflow control, and the assembly is compatible with the chemical | Cracking pressure, material, spring and seal compatibility, minimum submergence and whether it restricts flow |
| Complete Venturi suction assembly | The buyer wants the injector, suction tube, filter and fittings supplied as one matched kit | Actual suction conditions, tube length, filter position, flow range, pressure differential and replacement parts |
A screen is not a solubility fix. It can stop a particle from entering the suction line, but it cannot make an incompatible A/B concentrate stable or prevent precipitation downstream. The screen also becomes a new pressure-loss and maintenance point, so its size and cleaning interval must be specified.
The most common installation errors
- Measuring from the outside of the tank. A molded tank base or internal foot can make an outside measurement misleading. Measure from the actual internal low point where solids collect.
- Using the full-tank level as the operating level. The tube may be safely submerged at startup and exposed to air during the last part of the batch. Mark the minimum level on the tank or controller.
- Placing the strainer below a recirculation return. The return jet can lift settled solids directly toward the intake. Separate the return and pickup, or change the flow path.
- Letting the tube rest on the bottom after maintenance. Flexible tubing can move when a lid is opened or when the pump starts. Use a rigid pickup, clamp, weighted assembly or a documented bracket.
- Treating the filter as the only acceptance test. A clean filter does not prove that the pump is drawing the intended concentration. Check draw volume, air entry and the post-mixing measurement.
A field test that takes less than one batch
| Step | Action | Pass condition |
|---|---|---|
| 1. Mark the geometry | Mark bottom clearance, minimum liquid level, wall clearance and the return or inlet locations on the tank or drawing | An operator can see the required position without guessing |
| 2. Inspect the settled layer | Let a representative solution stand for the normal hold time, then record sediment depth and appearance | The selected clearance remains above the layer with margin |
| 3. Check submergence | Run the injector through the lowest planned operating level while watching the intake and suction line | No vortex, air bubbles or loss of prime occurs |
| 4. Measure the draw | Collect or weigh the solution removed during a timed interval at the normal operating point | The observed draw is repeatable and within the injector or pump setting tolerance |
| 5. Inspect downstream | Check the suction screen, filter, injection point and a representative emitter or sample after the test | No abnormal solids or air-related interruption is present |
Repeat the test after a formulation change, a new water source, a longer hold time or a change to the tank mixing method. The intake height is part of the process recipe, because the sediment layer and liquid-level profile are part of the process too.
What to put in an RFQ
| RFQ line | Ask the supplier to state |
|---|---|
| Tank geometry | Internal bottom shape, usable volume, access opening, outlet arrangement and the lowest operating level |
| Pickup assembly | Tube, strainer or foot-valve model, overall length, screen area, opening size, connection size and adjustment method |
| Chemical compatibility | Wetted materials and seal materials for the named fertilizer formulation, pH range, temperature and concentration |
| Hydraulics | Pump or Venturi suction requirement, maximum suction lift, allowable pressure loss, expected draw rate and priming behaviour |
| Maintenance | How the strainer is removed, how often it is cleaned, what replacement parts are available and how residue is disposed of |
| Acceptance evidence | A drawing or photo showing the installed clearance, a timed draw test and the operating range at minimum liquid level |
Sourcing candidates for the intake path
These offers are sourcing candidates for different intake roles, not approved recommendations. Marketplace data are supplier or platform statements. Exact strainer geometry, chemical compatibility, shipped variant and field performance require an RFQ plus a sample or bench test.
Bottom line
Approve the intake assembly only when the pickup height is shown on the tank drawing, remains above the observed sediment layer, stays submerged at the minimum operating level, is clear of turbulence, and can be removed and cleaned without losing its setting. A supplier's generic "filter" label proves none of those conditions. The final decision belongs to the buyer's formulation, tank geometry, pump or Venturi conditions and recorded draw test.
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