The platform: Surdial hydraulics by symbol, the blood-side modules, the power box and the maintenance modes
Identify the Surdial type, revision and mains rating, follow the fluid path from the RO water inlet to the drain by component symbol, name the blood-side modules and the boards that drive them, and know which maintenance mode shows what.
First identify which Surdial is in front of you
The Surdial is a single-patient haemodialysis machine that the manufacturer intends for hospital and home use. Level 1 gave you the general machine; this course is about where this one differs. The first difference is that 'Surdial' is not one machine. The service manual describes a Type I and a Type II, four electrical power box layouts (A to D), several generations of the main board, sub-board, bubble sensor board and dialysate pressure board, and software (ROM) versions from before 2.40 to 4.41 and later. Many settings, screens and spare parts depend on which combination you have.
So before you open a cover, write down four things: the machine type (the maintenance data screen shows it on later ROMs), the ROM version, the mains rating (110 V and 230 V machines carry different sub-boards, switching regulators and gear pumps) and the serial number. The manual uses serial number ranges to tell you which variant of a pump, valve or board was fitted at the factory. An order for a gear pump, a bellowphragm pump or a main board placed without these four facts is a gamble.
Be careful with the name. The newer Surdial X is a different machine with its own UF pump and its own field safety notices; do not carry its procedures or limits over to the older Surdial covered here, or the other way round. Notices also exist for the Surdial 55Plus (2025, P1 magnet gear pump), so check the regulators' notice lists for the exact model and serial in front of you.
Water side: from the RO inlet to deaerated, heated water
The manual's flow chart labels every component with a symbol, and the machine's own screens use the same symbols, so learn them. Treated (RO) water enters through the supply water filter F and the reducing valve PR, which brings the loop pressure down to a stable working value. The pressure switch PS confirms that water is actually arriving at sufficient pressure; when it drops out, the machine raises the short water supply alarm. Relief valve RV3 protects against excess supply pressure.
Temperature sensor T1 measures the incoming water. On machines with the heat exchanger option (HEX), the warm drain water preheats the incoming water. The heater H then warms the water; T2 measures the heater outlet and the temperature limit switch LS1 on the heater surface is an independent protection against overheating. The heater is mains-powered and is switched through a relay and a solid-state relay in the power box, which matters when you fault-find a heater that will not heat or will not stop.
Deaeration follows. The deaeration pump P1 draws water through the deaeration tank AS1 under negative pressure so that dissolved gas comes out of solution, with buffer tank BTW helping the process. Relief valve RV4 limits excess negative pressure and check valve C2 holds the negative pressure in the bellowphragm line. The gas leaves through the gas discharge valve V10 with flow-limiting connectors R2 and, on some machines, R3. Fitted or not, R3 changes the circuit, so the manual asks you to confirm it before working.
Preparation and balancing: the viscous chambers
The heart of the Surdial is a pair of chambers, VCa and VCb, which the manual calls viscous chambers. They contain a defined volume of silicone oil and are used in turn. Three-way valves V5 to V8 change over the fresh-fluid and drain sides of each chamber, and two bellowphragm pumps, VPa and VPb (also called viscous pumps), move the oil for each chamber. Photo-sensors PH1 to PH4 tell the main board where each bellowphragm pump is: one sensor per pump for the origin point and one for rotation. The manual does not describe the control principle in detail; what it does make clear is that the machine relies on a measured chamber capacity, a per-pulse volume for each viscous pump and a set of UF correction coefficients, all stored as machine-specific values. That is why chamber volume, silicone oil and these values come up again in every later lesson.
Concentrate enters through V13 (A concentrate), V14 (B concentrate) and, with the option, V17 for acetic acid. V12 opens the disinfectant concentrate line. The amount of each concentrate is set by dilution ratios stored separately for chamber A and chamber B, for each dialysis mode: two bicarbonate modes (BC1 and BC2) and an acetate mode (AC). Buffer tanks BTD1 and BTD2 mix the prepared dialysate before the conductivity cell CD, which sits together with temperature sensor T3. Remember the colour code the manual insists on: red connector for A, blue for B.
Downstream, the dialysate pump P2 drives the flow, the flow meter FM shows it, needle valve NV2 sets the dialysate flow and NV1 the priming flow. Relief valve RV1 controls priming pressure and RV2 dialysate pressure. Bypass valve V9 sends dialysate past the dialyser, with pinch cock PC1 and limiter R1 setting the bypass flow. The dialysate pressure sensor PD, check valve C1 and the coupler line filter F7 sit on the dialyser path; the coupler switch LS2 tells the machine whether the couplers are on the rinse port or on the dialyser. On the return side, the second deaeration tank AS2 with its float switch FSW, valve V4 and pinch cock PC2 removes gas from the dialysate, the blood leak sensor BLD watches the spent fluid, V3 opens the drain, V2 the priming line and V11 the rinse line. The sampling port SL is where you take dialysate for an independent conductivity check, and the flow sensor FS watches flow in the closed line.
Blood side
The blood pump BP is a roller pump with a cover switch BPC. The manual describes M3 and M4 pump types, and two rolling tube sizes: a standard tube and a smaller one. The tube type is a setting, the gap between rollers and housing is adjustable, and the pump flow calibration (gain and offset) is stored per machine and was determined with the manufacturer's standard blood line. A different or smaller line needs the gap and the calibration revisited.
Venous pressure is measured by the venous pressure board PV, which plugs onto the main board; the arterial pressure board PA is an option of the same design, and its mounting position and tubing decide which function it serves. The bubble detector BD on the venous line is served by the bubble sensor board, either the earlier SBY0160 or the later SBY0205, and the venous clamp CLV closes the line on alarm, with the clamp position sensor LS5 confirming that it has closed. The syringe (heparin) pump SP is an option with its own overload switch LS3; its rate assumes the manufacturer's syringe unless a syringe ratio is set.
Electronics and the power box
Most of the electronics live in the electrical power box. On one side you find the breaker, the power switch, the noise filter, the DC +24 V switching supply and the +5 V and ±12 V supply (a switching regulator or, on later machines, a converter board), the relay and solid-state relay for the heater, the sub-board and the fan; the D type box also has a transformer on 230 V machines and its own fuses. On the other side sit the main board with the venous (and optional arterial) pressure board, the DSUB board (or the VR board on the D type), the buzzer board, the optional battery and, on some boxes, the bubble sensor board.
The main board carries the microprocessor that runs the machine, keeps the settings in RAM and EEPROM, holds the ROM that defines the software version and has DIP switches that select some functions. Its terminal block TM1 takes T1, T2, T3 and the conductivity cell. The sub-board contains the drivers for the blood pump, syringe pump and both viscous pumps and switches the mains-powered loads: P1, P2, the heater and the fan. A 110 V machine and a 230 V machine use different sub-boards, so the board number matters. The operation panel board and a 40-character, four-line LCD complete the picture.
Treat the whole power box as live whenever the cord is in. The manual warns against touching non-isolated wiring and terminals, against touching boards with wet hands and requires the plug to be pulled before you touch a terminal block. In a machine that is full of water this is not a formality.
The maintenance modes: your window into the machine
The Surdial has ten maintenance modes. Some only display, some may be changed at any time, and some are protected and can be changed only when a protection setting is released. Access and release follow the manufacturer's procedure and belong to trained personnel; this course does not teach key sequences. What you need is to know what each mode is for.
Mode 1 shows live data: blood leak readings and auto-zero value, closed-circuit leak pressures for each chamber, conductivity and concentration, venous, arterial and dialysate pressure, TMP, the set and measured temperatures T1 to T3, the ROM version and, later, the machine type. Mode 2 holds alarm limits and the closed-circuit leak test levels. Mode 3 can force alarms off; the manual forbids using it during dialysis and forbids releasing the blood leak alarm during treatment, and you should treat any alarm left forced off as a serious finding. Mode 4 monitors switches and sensors and lets you run valves, pumps, the clamp and the fan by hand. Mode 5 holds concentrate data and the conductivity calibration. Mode 6 holds machine-specific values: pressure and temperature offsets, chamber volumes, viscous pump per-pulse volumes, UF coefficients, blood pump calibration, rolling tube type and heater control coefficients. Mode 7 holds system and option settings. Mode 8 counts operating hours and switching cycles of the pumps, fan, clamp and valves. Mode 9 runs the air purge (machine filling) procedure, and mode 10 shows the last 20 alarms with date, time and error number.
Two rules follow at once. Record every value in modes 2 and 5 to 7 on the manual's setting record sheet before you change anything, because several are unique to this machine. And never change a protected setting or run a component by hand with a patient connected: the manual classes both as a danger to the patient.
| Part | What it does | How it fails | |
|---|---|---|---|
| 01 | PR, PS, F (water inlet) | Filter, pressure reduction and confirmation that supply water is present | Clogged filter or weak supply gives short water supply alarms |
| 02 | H, T2, LS1 (heater) | Heats supply water; T2 measures outlet, LS1 limits surface temperature | Heater, relay or SSR fault; scale; T2 sensor error |
| 03 | P1, AS1 (deaeration) | Draws water under negative pressure to remove dissolved gas | Worn gear pump head, air in circuit, pump run dry |
| 04 | VCa, VCb with V5-V8 | Alternating viscous chambers that prepare and balance dialysate | Wrong silicone oil volume or air in oil: UF and conductivity errors |
| 05 | VPa, VPb with PH1-PH4 | Bellowphragm (viscous) pumps and their position sensors | Drive errors, dirty or misaligned photo-sensor, wrong type for ROM |
| 06 | V13, V14, V17, V12 | A, B, acetic acid and disinfectant concentrate inlet valves | Sticking valve or crystallised concentrate: conductivity drift |
| 07 | CD with T3 | Dialysate conductivity and temperature measurement | Deposits on electrodes, loose harness at TM1, drift |
| 08 | P2, FM, NV2, V9, PD | Dialysate pump, flow reading, flow setting, bypass and dialysate pressure | Pump wear, misadjusted needle valve, pressure sensor offset |
| 09 | AS2, FSW, BLD | Dialysate deaeration after the dialyser and blood leak detection | AS2 error, dirty blood leak window gives false blood leak |
| 10 | BP, PV, BD, CLV, SP | Blood pump, venous pressure, air detector, venous clamp, syringe pump | Roller gap, sensor drift, bubble board level, clamp leak |
Typical scenario: the right pump for the wrong machine
Typical scenario, not a recorded case. A clinic ordered a replacement dialysate gear pump for a Surdial by description only. The pump arrived, was fitted and ran, but it was the version for a different mains rating and the head was of the other type, whose spare kit does not fit the first. A second order was needed and the machine stood idle for two weeks. When the engineer finally read the type, ROM version, mains rating and serial number from the machine, the manual's serial number tables showed at once which pump, which spare kit and which sub-board belonged to it.
On the Surdial the serial number, type, ROM and mains rating decide the part. Read and record them before ordering anything.
Pump motor flooded on another dialysis machine
Engineers discussed a haemodialysis machine, model not recorded, whose pump motor had lost its seal so that water got inside. One option was to rebuild it: dismantle, clean the rotor and stator, fit new bearings and seals. The engineer who raised the question leaned towards replacing the motor, because a rebuilt motor in a wet machine is hard to trust and a failure would stop a treatment. The discussion did not reach a single answer, but agreed that the reason water reached the motor had to be found first.
On the Surdial too, the gear pumps and their motors sit next to water. Find the leak that wetted a motor before replacing it, and match the replacement to type and mains rating.
On-site checklist
- Machine type, ROM version, mains rating and serial number recorded
- Power box type (A to D) identified
- Bubble sensor board and dialysate pressure board generation noted
- R3 fitted or not confirmed
- Options noted: arterial pressure, syringe pump, battery, acid port, hot rinse, heat exchanger
- Settings in modes 2 and 5 to 7 copied to the setting record sheet
- Alarm history (mode 10) and operating counters (mode 8) read before any work