DIFFERENTIAL PRESSURE ADJUSTMENT Partner valve

Transcription

1 alancing part 7 TENIL FOUS DIFFERENTIL PRESSURE DJUSTMENT Partner valve The use of the ΔP regulators to keep the differential constant at the ends of a secondary circuit is usually accompanied by the installation of a manual balancing valve, this partner valve installed on the delivery line at the compensation valve installation on the return line. The partner valve is essentially a manual balancing valve fitted with an adjustable obturator through an external knob and two pressure test ports located at the obturator ends, which can be used for the connection capillary with the ΔP regulator valve. 3,,, 0, 3 0 The partner valve can be used with two different modes depending on how the capillary is connected before or after the obturator.

2 ONNETION WIT PILLRY DOWNSTREM TE OTURTOR With the capillary connected after the obturator, the partner valve is external to the circuit to which the ΔP is kept constant. y schematizing the secondary circuit as shown in the figure below, the partner valve does not have any influence within the controlled circuit. t the aforementioned circuit, the ΔP valve maintains a constant differential of ΔP OST and, as previously seen, the flow rate depends only on the Kv of the adjustment valve. The partner valve therefore contributes to reduce the differential given by the head of the primary circuit. ΔP VP ΔP cost ΔP OST ΔP ΔP In this configuration its application is a support to the ΔP regulator in order to keep the differential to be reduced at an acceptable value. The diagram below shows a circuit of a certain length where the head provided by the pump increases getting closer to the pump itself and at the same time there is an increase of the differential that the ΔP regulator valve has to reduce. s can be seen, switching from circuit to, the head that the valve ΔP has to compensate increases considerably: ΔP ΔP = = - 0 = kpa ΔP ΔP = = 0-0 = 30 kpa ΔP ΔP = = 80-0 = 70 kpa aving a fairly high differential already in the design conditions means letting the differential compensating valve work with the obturator very close to the seat; in this situation, in partial load conditions, the already very stressed valve may be forced to further reduce the bore cross section, thus failing to work in the best conditions On the circuit in consideration, a partner valve will be installed for each branch with the capillary connected downstream of the obturator. For a secondary circuit balanced by a ΔP valve, the minimum upstream head to operate the valve properly can approximate at one and a half the head value required for the circuit. =, ΔP =, 0 = kpa OST

3 Therefore under these conditions the ΔP =, MIN to be ΔP =, 0 = kpa OST "used" by the compensating valve is: = = 0 = kpa The partner valve setting is: ΔP S = - = = 0 kpa ΔP VP = - = = kpa ΔP VP = - = = kpa p (mm w.g.) 0,000 0,,, 3 3, 0 p (kpa) , ,000 0, PRTNER VLVE DJUSTMENT p (mm w.g.) 0,000 0,,, 3 3, p (kpa) 00 The 00valve must be adjusted using the Kv diagrams. In the case of circuit, for a design flow rate of l/h, the partner valve must introduce a 0 kpa load loss. 0 s indicated by the diagram, the partner valve 0, 0,0 0, must be set to the 0,3 0,, 0 "," position, with a Kv value of 0,9 m 3 G (m /h. 3 /h),000,000, setting position Kv (m 3 /h) 0,,, 3 3, (Kvs) 0,3 0, 0,9,38,7,,8,9 00 circuit circuit circuit Within the individual secondary circuits, the pressures distribution will be:, ,0 0, 0,3 0, 0,, 0 setting position 0,,, 3 3, (Kvs) Kv (m 3 /h) 0,3 0, 0,9,38,7,,8,9 0, G (m 3 /h) kpa 0 kpa s can be seen, the ΔP regulators are configured to work all under the same design conditions.

4 ONNETION WIT PILLRY UPSTREM OF TE OTURTOR. Unlike the previous case, when the capillary is connected before the obturator, the partner valve is an integral part of the circuit whose ΔP is kept constant by the differential regulator. If the secondary circuit is schematized as in the following figure, the partner valve has a direct influence within the controlled circuit, whose ΔP valve ends maintains a constant differential ofδp OST. To exemplify the situation it is hypothesized that the secondary circuit to be controlled with the ΔP valve is composed of three identical circuits connected by a vertical distribution. ΔP cost SEONDRY IRUIT The nominal flow rate of nominal load loss of 0 kpa is the design data of the individual circuit. The vertical distribution causes a kpa load loss for each connection section. Therefore the secondary circuits and are subjected to a head of = kpa and = kpa. head other than the nominal head causes a greater flow rate in the individual circuits than the design flow rate, which can be calculated with the balancing factor F. IRUIT WIT ΔP REGULTOR To make the secondary circuit independent of the head variations of the primary circuit, the circuit is balanced with a differential compensating valve. The reference positions for setting the ΔP regulator could be kpa (not recommended because below the nominal value) or at 0 kpa. In the case of a differential compensating valve set at 0 kpa, the overall flow rate for the secondary circuit is as follows: F = 0, 0, = =, 0 0, 0 0, G = G = 990 = 0 l/h G = F G =, 300 = 0 0, 0, F = = =, 0 G = F G =, 300 = 30 l/h, 30 l/h 0, 37 l/h 30 l/h 30 l/h 7, 0 l/h 37 l/h 0 l/h 30 l/h 7, 0 0 l/h 0 kpa

5 IRUIT WIT ΔP REGULTOR ND LNING VLVE ON SINGLE IRUIT In these conditions, an appropriate solution would be to insert a manual balancing valve on each individual circuit, set so as to return the design flow rate to the nominal value. IRUIT WIT ΔP REGULTOR ND PRTNER VLVE If the insertion of balancing valves is not possible, the partner valve connected to the upstream capillary can be used. In this case, the setting must be equal to the difference between the setting value of the differential compensating valve (0 kpa) and the nominal load loss of the circuit ( kpa). of partner valve = 0 - = kpa l/h 8 30 l/h 0 0 kpa The head unbalancing caused by the internal distribution of the secondary circuit are not balanced in this configuration. 0 0 kpa ONLUSION Depending on how it is connected to the differential compensating valve, the partner valve has two completely different functions: With the capillary connected downstream of the obturator the load loss that the partner valve introduces is not part of the secondary circuit controlled by the ΔP valve but of the primary circuit. Its function, in this case, is to prevent the ΔP regulator from working with the obturator too close to the closing position With the capillary connected upstream of the obturator the partner valve is an integral part of the circuit controlled by the differential compensating valve and has the function of "refining" the differential compensating valve setting as much as possible to the nominal value, adjusting the flow rate accordingly. REFERENE DOUMENT: TE. ROURE 00 Visit aleffi on YouTube youtube/aleffivideoprojects 087G WE RESERVE TE RIGT TO MKE NGES ND IMPROVEMENTS TO TE PRODUTS ND RELTED DT IN TIS PULITION, T NY TIME ND WITOUT PRIOR NOTIE. aleffi S.p.. S.R. 9 n. 800 Fontaneto d gogna (NO) Italy Tel Fax info@caleffi.com opyright 07 aleffi