Total dynamic head is the bridge between field piping and pump selection. Without TDH, pump selection becomes a guess dressed as a specification.
TDH components
TDH is the total head the pump must add to the fluid to satisfy the installed system. It includes elevation, required discharge pressure, pipe friction and local losses through elbows, tees, valves, reducers, hoses and manifolds.
TDH = H_static + H_pressure + H_friction + H_minorUse consistent units. For field oilfield work, feet of fluid head is usually easiest because pump curves are commonly read that way.Pressure head conversion
H_pressure (ft) = psi × 2.31 / SGExample: a hydrocyclone manifold requiring 35 psi at SG 1.20 needs 67.4 ft of pressure head at the manifold.Friction loss logic
Friction loss rises strongly with velocity. A line that looks acceptable at low flow can become the entire reason the pump misses its duty when flow is increased.
Velocity (ft/s) = 0.4085 × Flow (gpm) / ID² (in²)Example: 800 gpm through 6 in ID gives about 9.1 ft/s. The same 800 gpm through 4 in ID gives about 20.4 ft/s, a very different loss and erosion picture.Worked TDH example
| Component | Value | Comment |
|---|---|---|
| Static elevation | 8 ft | Tank level to discharge point |
| Required manifold pressure | 35 psi at SG 1.20 = 67.4 ft | Process energy |
| Pipe friction | 14 ft | Flow and line-size dependent |
| Minor losses | 6 ft | Valves, elbows, reducer, hose |
| Total TDH | 95.4 ft | Pump curve must support flow at this head |
Building the system curve
A system curve plots required head against flow. Static head stays nearly fixed, but friction increases approximately with flow squared in turbulent flow. That shape explains why small flow increases can require much more head.
H_system ≈ H_static + K × Q²K is the installed-system resistance. It changes with line size, roughness, valve position, fittings, hose condition and mud properties.Common TDH mistakes
Acceptance test
Measure suction condition, discharge pressure, downstream pressure and, where possible, flow. If the field operating point is not near the calculated curve point, look for wrong rotation, worn impeller, air entry, blocked line, valve position or wrong impeller trim.
Engineering depth: separating process head from piping loss
Do not mix process pressure and piping loss into one unexplained number. A hydrocyclone may need a target pressure at the manifold, while the pump also has to overcome the losses between suction and that manifold. Keeping the terms separate makes troubleshooting much cleaner.
| Term | Where measured | Troubleshooting value |
|---|---|---|
| Process pressure | At manifold or user point | Shows whether downstream equipment receives energy |
| Discharge pressure | At pump discharge | Includes process demand plus line loss |
| Friction loss | Between pump and user point | Reveals undersized hose, blocked valves or poor routing |
| Static head | Elevation difference | Usually fixed unless tank level changes |
If pump discharge pressure is high but manifold pressure is low, the line is consuming the energy. If both are low, look at pump curve, suction, speed, rotation or wear.
Related reading
TDH Field Envelope
TDH must include every part of the route that consumes head: static lift, pressure requirement, friction loss, elbows, valves, hose, manifolds and downstream equipment. Missing one temporary hose or valve can move the selected pump away from its real duty.
TDH = static lift + pressure head + friction head + minor lossesUse mud SG when converting pressure to head or head to pressure.| TDH and System Head Curve for Drilling Fluid Pumps check | Required field evidence | Stop or redesign trigger |
|---|---|---|
| Duty definition | flow, head, speed, density correction, motor load and the installed system curve are recorded with units and operating state. | The duty is described only by equipment name or nameplate capacity. |
| Installed-route confirmation | Line length, elevation, valves, receiving point and material condition are checked. | The route cannot be restarted or isolated safely after a stop. |
| Process acceptance | The downstream process becomes stable after the correction. | One gauge improves while flow, quality or reliability gets worse. |
