The pre-settable Axial design PICV is selected when either a manually operated valve is required or when a choice of electric actuation is preferred.
- The rising stem design ensures that valve stroke is maintained even when the valve is pre-set (with no loss of stroke)
- Flow rates can be adjusted and valves locked in position, even with the actuator in place
- Linear temperature control is achieved because of the equal percentage control characteristic of the valve, when used with 0-10v actuators
- The Axial PICV is maintenance free and uni-directional; suitable for installation in either the flow or return pipework providing the flow direction arrow is correctly observed.
- Strainers should be installed up-stream of the PICV in order to prevent ingress of dirt.
- The valve body is manufactured in dezincification resistant brass (DZR) and is currently available in 4 sizes, DN15, DN20, DN25 and DN32.
Axial PICV valves can be supplied separately or can be incorporated into the Xterminator® range of engineered terminal unit connection sets to optimise and maintain control of a fan coil, chilled beam or other hydronic unit.
These can be configured for horizontal, left or right hand access dependent upon where the fan coil is to be mounted.
Valve Setting & Flow Rate Adjustment – Manual Valves
The black hand-wheel and the integrated setting ring are used for valve setting and flow rate adjustment.
To set the flow, firstly calculate the design flow rate (expressed as a percentage of the valves maximum nominal flow rate).
A locking pin secures the hand-wheel in place. Lift the locking pin to unlock the hand-wheel. The hand-wheel is graduated in 10-degree intervals from 100% to 10%. Rotate the hand-wheel to the calculated percentage as indicated by the locking pin. Depress the lock pin to lock and set the hand-wheel in the desired position.
The valve is actuated by means of an electromotive actuator, a thermoelectric actuator or a TRV sensor.
Flushing and Media Quality
Systems should be cleaned and flushed as detailed in the BSRIA guide Pre commission cleaning of pipework systems (BG29/2012).
Water quality should also be maintained to the standards referred to in BSRIA guide Water treatment for building services systems (AG2/93).
The compatibility of cleaning agents and water treatments should be checked with Marflow prior to use with the product.
When the PICV is mounted in the flow pipe-work, flushing should be avoided and by-passes used to drain prior to back and then forward flushing the system.
Strainers should be installed up-stream of the PICV in order to prevent ingress of dirt.
For further detailed information or a step-by-step guide to flushing the system, please contact Marflow Hydronics.
Verification of Flow Rates
Test points are included in the design of the PICV for measurement of differential pressure in order to verify that the valve is operating correctly. Providing the measured differential pressure is between the upper and lower differential pressure limits (20kPa and 400kPa), then the valve can be assumed to be working correctly and within its operating range. It should be noted that the test points cannot be used to measure flow rate across the PICV. Should flow measurement be required, then a separate orifice plate or venturi should be installed downstream of the valve and used to verify this.
CIBSE Commissioning Code W (2010), section W7.7.3, should be referred to for guidance, if verification of flow is required.
Prior to verification the following procedures should be followed:
- Check that the pump has been correctly sized.
- Ensure that the system is clean, has been flushed and is free of air.
- Strainers have been checked and are clean (and have been so for at least 24 hours with the pump in operation).
- Ensure that all actuators are fully open
Flow can be verified in two ways:
- Calculation of flow at the branch or sub-circuits: All PICVs can be confirmed as working efficiently and correctly if the flow measured independently, at the branches and sub-mains, is within ±10% of design flow rate.Since the PICV works as a constant flow regulator then the flow at the branch or sub-circuit can be calculated as the sum of all flows downstream of the branch or sub-circuit measuring device. This can be verified further if required by flow measurement at the terminal unit.
- Flow measurement at the terminal unit:For verification it is usual to only sample or batch test flows at a percentage of installed terminal units although it may be preferable to have the facility to check flows at all terminal units should it be required (providing a separate metering station or venturi has been installed).
Optimisation of Energy and Cost Reduction
Once flows have been verified as being within the required tolerances to design flow rate, then pump speed can be reduced in order to optimise energy efficiency.
After the “index circuit” has been identified, then the pump speed can be reduced until the pressure drop across the PICV in this circuit is equal to or just above the start up pressure for the valve. The “index circuit” is generally the one with the lowest differential pressure across the PICV.
For full information on PICVs, download our Definitive Guide to Pressure Independent Control Valves