BTMS Pump Head and Pressure Drop: An OEM Review Guide

Even if the Battery Thermal Management System (BTMS) has sufficient rated cooling capacity, temperature control of the battery pack may still be suboptimal if the cooling circuit fails to deliver the required flow rate under the actual pressure drop conditions encountered in the installation. For electric buses or lorries, the water pump head, pipework layout, valves, coolant viscosity and flow balance across the parallel branches must be assessed comprehensively as a unified hydraulic system.

This guide sets out the input parameters that original equipment manufacturers (OEMs) should clarify and finalise before requiring BTMS suppliers to confirm the water pump’s operating point. This guide does not specify standard flow or pressure values, as these parameters depend on the specific battery pack, coolant, piping system and operating conditions.

The assessment should be based on the vehicle’s cooling circuit as a whole, rather than relying solely on the water pump’s nameplate specifications

The maximum flow rate and maximum head of a water pump are typically at opposite ends of its performance curve; neither value alone can determine the actual operating point following installation. A comprehensive circuit diagram should be prepared, clearly identifying components such as the BTMS, battery cold plates, manifolds, hoses, valves, filters, height differences and all shared branches.

Request pressure drop data from component suppliers for specific coolant temperatures and flow rates. Sum the individual pressure losses under uniform boundary conditions, taking into account the status of all controllable valves. If validated data is lacking for a particular component, it should be marked as ‘to be determined’; under no circumstances should overly optimistic estimates be entered arbitrarily.

Verify the complete water pump performance curve

The expected operating point is the intersection of the water pump performance curve and the system resistance curve. This intersection point should be evaluated at the specified speed and supply voltage, rather than simply referring to the pump’s nominal ratings. At the same time, it is necessary to confirm whether the performance curves provided correspond to the actual coolant mix ratio and temperature range used.

Low-temperature coolant increases hydraulic resistance. For low-temperature operating conditions, suppliers should be asked to provide performance data at representative fluid temperatures and concentrations. If the cooling circuit contains ethylene glycol, never directly apply performance curves intended for pure water conditions; always seek confirmation from the supplier first.

Clarify flow rates for each branch and requirements under different operating modes

Focusing solely on the total flow rate may mask issues of insufficient flow in battery branches. Acceptance criteria for required flow rates or flow distribution should be clearly defined for each critical path and under different operating modes (such as charging, driving, pre-conditioning, and circulation conditions during shutdown or maintenance).

• Specify each parallel branch and its balancing method.
• Indicate which valves and pumps are active in each operating mode.
• Specify measurement points and sensor accuracy requirements.
• Record permissible electrical power consumption and noise limits.
• Specify the type of coolant and the filling/venting procedures.

Distinguish between ‘air-related issues’ and ‘pump selection issues’

Air entrapped in the pipework reduces effective flow rate, generates noise and causes unstable pressure readings. Before ruling out a pump selection, please ensure that the system has been filled with coolant and bled in accordance with established specifications. Please refer to the accompanying ‘BTMS (Battery Thermal Management System) Cooling Circuit Bleeding Checklist’.

If air accumulates repeatedly, this may indicate issues with the pipework layout, expansion tank, venting devices or seals. Simply increasing the pump’s operating parameters (speed/power) will not fundamentally resolve the problem.

Verification of Actual Installation Operating Conditions

During the commissioning phase, the pump’s operating parameters, supply voltage, coolant temperature, and flow and pressure data measured at specified locations should be recorded. Compare the measured results with the approved hydraulic model or the performance curves provided by the supplier. Furthermore, verification must be carried out under operating conditions involving valve position changes or the activation and deactivation of cooling branches.

‘Temperature uniformity’ remains a core metric for system-level acceptance. During evaluation, hydraulic data, battery pack inlet and outlet temperatures, and sensor distribution data should be considered comprehensively; flow rate readings alone cannot demonstrate the uniformity of cell cooling.

Provide a comprehensive hydraulic system Request for Quotation (RFQ) documentation package

The documentation package should include: circuit schematics, coolant specifications, temperature ranges, pressure drop data for each component, target flow rates under different operating conditions, voltage ranges, installation constraints, and validation requirements. This will enable the EVLINK team to evaluate BTMS solutions based on the vehicle’s actual operating conditions (rather than relying solely on isolated parameter points from product catalogues).

Submit a BTMS hydraulic evaluation request, specifying any input parameters that remain undefined. The final deliverables should include: traceable operating point decisions based on clear assumptions, as well as a corresponding vehicle validation plan.