REGULATOR SIZING - Steam Specialty

1 REGULATORSIZING- 107 -DEFINITIONSRELATING TOREGULATORCAPACITYThe capacities contained in this bulletin are based on a specificlevel of performance by the REGULATOR . The measure of perform-ance is accuracy of regulation, also known as offset or table is appended with a footnote indicating the accuracyof regulation obtainable at the rated capacities terms involved in the determination of accuracy ofregulation and rated capacity are defined as follows:* REGULATED VARIABLEis the controlled condition of thefluid either (1) flowing through a REGULATOR or (2) in a processserved by a REGULATOR . Reduced pressure, back pressure anddifferential pressure are the typical regulated variables to bedealt with in this instance.

2 Other cases, such as vapor pressureproduced by a Steam -heated vapor generator, will be found.* MINIMUM CONTROLLED FLOWis the lowest flow at whicha steady condition of fluid pressure can be maintained. Anyfurther reduction of flow produces a noticeable deviation of theregulated pressure toward dead-end shut off. For convenience,minimum controlled flow is often considered as being at 5% ofrated capacity.* SET POINTis the value of the regulated pressure at minimumcontrolled flow.* RATED CAPACITY of a pressure REGULATOR pertains to specifiedinlet and outlet conditions and is the rate of flow through theregulator, guaranteed by the manufacturer, when the regulatedpressure deviates no more than a specified number of psi fromthe set pressure at minimum controlled flow.

3 * ACCURACY OF REGULATIONis the amount by which theregulated pressure deviates from set point at minimumcontrolled flow as the flow through the REGULATOR is graduallyincreased from minimum to rated capacity.*LOCK-UPis the increase from set value due to dead end shut-off.* Adapted from Definitions of REGULATOR Capacities , StandardNo. FCI 58-1, published by Fluid Controls Institute, - PERCENTREDUCED PRESSURE - psiTYPICAL REGULATION CURVESPENCE TYPE EDINLET PRESSURE 100 psiNOTES ONUSE OFTABLESThe lowest reduced pressures are approximate critical appreciable increase in flow can be obtained at lower pipe size should be enlarged at REGULATOR outlet toapproximately equalize pipe velocities before and after thereduction.

4 The Steam Capacity Tables are useful for determiningsteam pipe sizes and REGULATOR size at any desired lower Seats Spence regulators are available with a choiceof seat sizes called Full and Normal Ports. There is a capacitytable for each port with standard plugs. The Cv Valve Coefficientsshown on the back page, indicate where 75% and 50%parabolic plugs are available. For a given pressure drop, ratedflows with various ports and plugs in the same size body may becompared. Thus, valve and port size may be selected to limitvelocities entering and leaving the REGULATOR . Lower velocitiesmean a greater proportion of the pressure drop occurs at thevalve seat, where it belongs, rather than in the body outlet andconnected ratings apply to Spence regulators with Type D, N andQ Pilots which are spring loaded and have 31/2inch pilots having greater or lesser sensitivity will provideproportionally greater or less accuracy of performance characteristic of a Spence Pressure Regulatoris shown above.

5 Using this curve to illustrate several terms ofreference, the following facts are evident:REGULATED VARIABLEREDUCED PRESSUREM inimum Controlled Point .. Pressure at Rated (100%) Flow .. psiAccuracy of Regulation, psi .. psiAccuracy of Regulation, % of set pressure ..10%The slight slope of the curve establishes a definite relationshipbetween flow and regulated pressure. Note that 1 psi accuracyof regulation is obtainable at 95% of rated back pressure regulation, or differential where the regulatoropens on increasing differential, the characteristic curve would lieopposite to that shown. It would slope upward with flow increasebecause a positive deviation is required to cancel valve PLANNING THE the valve in a straight run of horizontal pipe.

6 See Fig. headroom above the valve for access through the blindflange. Provide clearance for stem withdrawal water hammer and erratic operation by installingtraps to provide proper drainage before and after the valve,and before secondary PRV or control damaging affects of scale and dirt in pipe lines byusing a strainer as shown in Fig. 1 . a 3-valve by-pass to facilitate inspection withoutinterrupting eliminate excessive noise and erratic regulation withsteam and other compressible fluids enlarge the deliverypipe size to effect a reasonable flow velocity at the reducedpressure. A tapered transition is recommended. If possible,avoid a sharp turn close to the REGULATOR outlet and a bull-headed tee connection to the low pressure initial and delivery pressure gauges to indicateperformance.

7 If the pressure rating of the delivery system orconnected equipment is less than the initial Steam pressure,provide a safety CONTROL 1/4 pipe for this line which connects the pilot diaphragmchamber to the desired point of pressure control. See Fig. the control at a point of minimum turbulence. Avoidcontrol immediately at the valve outlet or after a turn. Whenthe delivery pipe expands in size select a spot at least 4 pipediameters beyond the point of away from pilot to avoid erratic operation and water delivery pressure gauge in control pipe to showpressure actually reaching pilot DESIGN GUIDELINES TO MINIMIZE the REGULATOR to provide a maximum inlet velocity ofabout 10,000 the REGULATOR outlet velocity.

8 If it would exceed30,000 FPM, use a Spence muffling orifice or a second stageregulator. 3 Expand REGULATOR outlet piping to limit discharge line velocityto about 10,000 abrupt changes in pipe size. Limit pipe diameterchanges to two pipe sizes per stage of expansion. Do notuse eccentric changes in downstream piping should be madeonly after the line size has been increased. Use long radiusfittings; avoid bull-head tee as much straight run of pipe on both sides ofregulator as possible:a - 10 pipe diameters minimum to the - 20 pipe diameters minimum of expanded line size fromthe all piping components, including strainer and stop valvesfor a maximum flow velocity of about 10,000 FPM (Exception:An outlet stop valve mounted at the REGULATOR outlet shouldbe equal in size to the REGULATOR ).

9 In areas where low soundlevels are specified, reduce this limit by 25% to 50%. limit noise transmission through the building s the REGULATOR and piping at least 3 feet away from solidsurfaces. Use sound-isolating piping high density insulation to the REGULATOR body, piping andsystem components. Insulation reduces heat loss significantlyand can provide moderate (3-6 dB) local noise Use a Spence noise suppressor to reduce the propagationof noise via the downstream Inlet Pipe2. Isolation Valve3. Strainer4. PRV Type5. Bypass Pipe6. Bypass Valve7. Delivery Pipe8. SRV Type9. Drip Pan Elbow10. Vent Stack11. Low Pressure Trap12. High Pressure Trap 1242121193561078d1d210 d120 d2 Min. 4 d2 Provide as much straight run of pipe on both sides of REGULATOR as possible: 10 pipe diameters minimum to the inlet.

10 20 pipe diameters minimum of expanded line size from the FORMAINVALVESELECTIONRULES FORMAINVALVESELECTION STEAMSERVICERULES FORMAINVALVESELECTION AIRSERVICERULES FORMAINVALVESELECTION WATERSERVICEWhen you select a Main Valve, your SIZING can be based onone of three methods. They are:ECONOMICALMAINVALVEE conomical Main Valve Selection is choosing a REGULATOR thathas the line size and rough capacity to handle the load. Noconsideration is given to velocities or noise. If you areinterested in an economical selection, select a REGULATOR typefor your application, then go to the Capacity Tables and selectthe size that will provide you with the capacity Main Valve Selection takes into consideration theinlet and outlet velocities of the REGULATOR , It will limit thesevelocities to acceptable standards.