الوصف
A fan that turns too slowly is usually blamed on the motor. On the DX380, DX420 and DX500 it is at least as often the pump feeding it. This unit is the hydraulic fan drive pump: it takes mechanical input from the gear pump train and delivers the variable flow that sets fan speed. When its displacement control drifts or its internal clearances wear, the fan cannot reach high speed even though the motor itself is still sound, and the machine cooks.
What we are selling here
A new HTD-branded pump made in China, dimensionally and functionally matched to the A10VSO18 size 18 variable displacement axial piston platform used in these Doosan fan circuits. It is an aftermarket substitute, not a genuine Bosch Rexroth component and not a genuine Doosan or Develon part. We list the reference figures below so your workshop can compare the duty limits against the original equipment rather than take a photograph on trust.
Reference data for the size 18 platform
Values from the Bosch Rexroth variable axial piston pump data sheet RA 92 711 for the (A)A10VSO series 31, size 18:
| المعلمة | Figure | Why it matters on an excavator |
|---|---|---|
| Geometric displacement | 18 cm3/rev | Sets the ceiling on fan motor speed at a given drive rpm |
| Maximum continuous pressure, port B | 280 bar (4,000 psi) | Covers full fan load in hot ambient conditions with the A/C running |
| Peak pressure | 350 bar (5,100 psi) | Transient headroom; repeated spikes above this shorten seal life |
| Inlet pressure range (port S, absolute) | 0.8 to 30 bar | Cavitation starts if suction is restricted by a collapsed line or blocked tank filter |
| Case drain limit | 0.5 bar above inlet, maximum 2 bar absolute | A pinched drain line is the most common cause of early rear seal failure |
| Maximum fluid temperature | 90 C (195 F) | Oil above this thins the film and accelerates wear in the control piston |
| Required cleanliness | 20/18/15 to ISO 4406 | Change the filter element and flush the circuit at fitting, every time |
Control variants: check yours before you order
Two pumps with the same housing and the same shaft can behave completely differently once fitted, because the regulator decides when the pump swings from full to minimum displacement. The published control families for this platform are:
| Control | What it does | Typical complaint when it is wrong or worn |
|---|---|---|
| DG | Two position, direct: jumps between maximum and minimum delivery when pilot pressure arrives at port X | Fan stuck at one speed, either noisy and cold or slow and hot |
| DR | Pressure control: delivers only the flow needed to hold the set pressure | Hunting, heat build-up, higher fuel burn at idle |
| DRG | Pressure control with remote pilot signal | No response to the machine’s temperature logic |
| DFR / DFR1 | Combined pressure and flow control | Slow fan response as engine load rises; DFR1 also blanks the orifice between port X and tank |
If you can send a clear photo of the regulator side of the old pump we will match it. Guessing here is the single most common reason a fan pump goes back.
Fitment
Listed for Doosan DX380, DX420, DX500 and DX520 excavator cooling fan circuits. The pump pairs with the K1057295 fan motor on many of these machines; if the motor has already been replaced and the temperature problem stayed, the pump is the next item on the list, and if the pump was changed and the fault moved, check the fan motor side of the circuit instead. Our excavator hydraulic pump range covers main pumps and gear pumps for the same machine.
What a worn fan pump actually feels like
Fan speed stops rising when the operator selects high idle. Coolant temperature drifts up during long loading cycles but falls back during travel. Swing and boom functions remain normal because they are on a different circuit. If the machine also lost power or the oil smells burnt, look upstream: fan pump diagnosis walks through the flow and pressure tests, regulator diagnosis and adjustment covers the control signal, and drive gear inspection is the check to run before you condemn a replacement pump that was starved by a failed transfer case. For procurement teams comparing specifications across brands, the pump buyer’s and specification guide is the reference we ask buyers to read first.
Fitting and commissioning sequence
- Confirm the control variant, spline form, flange pilot diameter and port thread sizes against the removed pump, not against a catalogue photo.
- Drain the fan circuit and replace the filter element. Refitting a clean pump to dirty oil voids the point of the job.
- Fill the pump casing with clean hydraulic oil through the case drain or suction line before starting. Dry starting an axial piston unit at first crank is a known killer.
- Connect the case drain line direct to tank with no restriction and no check valve in that path, keeping within the 2 bar absolute limit.
- Crack the suction line briefly to purge air, then run at low idle while you check for leaks at every joint.
- Bring the machine to operating temperature and prove the fan responds: cover part of the radiator or raise the hydraulic oil temperature deliberately and watch fan speed increase.
- Record coolant and hydraulic oil temperatures at low idle and high idle, both before and after the work. This is the evidence you need if a claim is ever made.
Warranty for new aftermarket units is three to six months as stated on your proforma invoice. Genuine OEM parts and used cores are sold without warranty. Packing is a wooden case as standard, or to your specification, and we send inspection photographs for confirmation before the box is closed.
