A desander feed pump is successful only when the desander cones receive enough stable energy to make the intended coarse-solids cut. The pump is not judged by nameplate flow; it is judged by manifold head, underflow character, suction stability and whether coarse drilled solids leave before they degrade.
Core calculation: pressure to head
Hydrocyclone feed pressure is usually read as pressure, but the pump curve is read as head. Convert pressure into equivalent head using the actual mud specific gravity.
Head (ft) = Pressure (psi) × 2.31 / SGExample: 35 psi at SG 1.20 gives 35 × 2.31 / 1.20 = 67.4 ft of head at the manifold.If the pump curve cannot deliver the required flow at that head after suction and discharge losses, the desander may run but it will not separate correctly.
Worked example: cone count and pump duty
Assume a desander bank has two 10 in cones, each expected to process about 500 gpm at the target feed condition. The manifold target is 35 psi and mud SG is 1.20. Required process flow is about 1,000 gpm, and the manifold head target is about 67 ft before adding line losses.
| Item | Value | Meaning |
|---|---|---|
| Cone count | 2 × 10 in | Approximate process demand: 1,000 gpm |
| Feed pressure | 35 psi | Equivalent to 67.4 ft at SG 1.20 |
| Line and manifold loss | Site-specific | Add to pump TDH, not to cone pressure reading |
| Acceptance check | Stable spray underflow | Confirms the cones are not starving or roping |
Acceptance criteria in the field
| Check | Good sign | Red flag |
|---|---|---|
| Feed pressure | Stable at the manifold target for the active cone count | Pressure swings with tank level or other pumps starting |
| Underflow | Open spray, not a tight rope | Rope discharge, no discharge or intermittent surging |
| Overflow | No obvious coarse solids carryover trend | Sand content or coarse return remains high |
| Suction | Flooded, quiet, no vortexing | Cavitation noise, air entry or collapsing hose |
Decision path
What makes this different from generic pump selection
The desander feed pump is a separation-control device. A transfer pump can be acceptable with approximate flow; a desander feed pump needs enough energy at the manifold to create centrifugal separation inside the cones. This is why the duty must be checked as both a pump-delivery problem and a hydrocyclone-separation problem.
Extra calculation: pump hydraulic power
After pressure is converted to head, the next check is whether the motor can support the duty at the actual mud density. Hydraulic horsepower is a screening number; final motor sizing still needs efficiency and service factor.
Hydraulic HP = Flow (gpm) × Head (ft) × SG / 3960Example: 1,000 gpm at 67.4 ft and SG 1.20 gives 20.4 hydraulic HP before pump efficiency. At 60% efficiency, shaft demand is about 34 HP before service margin.This is why a desander pump that looks adequate on clean-water flow can become marginal after mud weight, suction losses and manifold losses are included.
Engineering notes that prevent false diagnosis
- Do not compare desander pressure between wells without correcting for mud specific gravity.
- Do not judge the pump from discharge pressure alone; cone underflow pattern and solids trend are part of the acceptance test.
- If blanking cones raises pressure and improves underflow, the pump may be short on head or flow for the full cone count.
- If pressure is correct but coarse solids remain high, check shaker bypass, cone wear, apex condition and whether the desander is processing representative flow.
Engineering depth: what to trend during a desander test
A desander feed pump should be commissioned against a short trend, not one pressure reading. Record tank level, pump speed, discharge pressure, manifold pressure, motor current, active cone count, underflow condition and overflow sand trend at the same time. If these values are not synchronized, the diagnosis can point in the wrong direction.
| Trend item | Why it matters | Interpretation |
|---|---|---|
| Manifold pressure | Confirms energy delivered to cones | Low pressure can mean pump, suction or too many active cones |
| Motor current | Shows real load | High current with poor pressure suggests restriction or wrong operating point |
| Underflow form | Shows cone health | Spray, rope and no-discharge mean different failures |
| Sand content trend | Confirms separation result | Pressure is not useful if solids removal is not improving |
Cone loading check = measured pump flow / active cone countUse the actual cone data for the installed hydrocyclone. The calculation is a field sanity check, not a universal cone rating.The strongest field test is controlled isolation: change one cone or one valve state at a time, wait for stabilization, then record pressure and underflow. Random valve changes create noise, not evidence.
