SV604 Flanged Full-Lift Safety Valve

SV604 full-lift flanged safety valve

The Spirax Sarco SV604 is a carbon-steel full-lift flanged safety valve for protecting pressure equipment and process systems from overpressure. It is documented for steam, inert industrial gas and water service, with inlet sizes from DN20 to DN150 and flanged connection arrangements for PN40 or ASME 300 inlet service. The outlet is selected as PN16 for the PN route or ASME 150 for the ASME route. This combination gives plant designers a clear route from the protected-equipment limit to the valve size, set pressure, discharge arrangement and certification required for the duty.

SV604 is a model-level safety valve selection rather than a generic relief-device description. The applicable pressure/temperature graph, set-pressure range, relieving medium, overpressure allowance, backpressure and bonnet or spring configuration must all be checked together. The figures and detailed tables below are therefore part of the engineering selection record, not a substitute for sizing the complete installation.

Product role and application

A full-lift safety valve opens rapidly when the protected system reaches its set pressure, providing the relieving area needed to control an overpressure event. SV604 is intended for duties such as steam boilers, steam and utility pipelines, pressure vessels, compressors, receivers and general process equipment. It can also be considered for inert industrial gas and water duties when the fluid, temperature, pressure and discharge arrangement have been checked against the data sheet.

For a steam system, the safety valve is commonly installed at the protected vessel or in a suitable steam line, including downstream of a pressure-reducing valve station where a regulator failure could expose downstream equipment to excessive pressure. For a Spirax Sarco SV604 selection, the valve must discharge to a safe location. A discharge pipe that is too small, poorly supported or exposed to excessive backpressure can change the relieving behaviour and impose damaging loads on the valve, so the complete piping layout is part of the selection.

Other media are not automatically covered by the words “water” or “gas”. Chemical compatibility, phase behaviour, contamination risk, temperature excursions and the applicable local rules must be reviewed with the manufacturer where the service is outside the stated range. The model should not be selected solely from the nominal pipe size or from a maximum pressure number.

Carbon-steel construction and configuration choices

The SV604 body and bonnet are carbon steel, with stainless-steel working components specified by size and component. The documented construction includes a stainless-steel seat, hardened stainless-steel disc options, a stainless-steel stem and skirt, and a spring selected for the pressure and temperature duty. This construction provides a robust flanged pressure boundary while leaving the set-pressure and configuration decision visible to the engineer responsible for the installation.

The ordering guide identifies closed-bonnet/easing-lever, closed-bonnet/sealed-cap, closed-bonnet/packed-lever and open-bonnet/easing-lever configurations. The packed lever is limited to DN20–DN100. A tungsten-alloy spring is required in the high-temperature region identified by the technical data and is available with the open-bonnet configuration. Open-bonnet valves are recommended for steam-boiler applications. The correct configuration therefore depends on the service, the temperature envelope, the need for manual testing and the safety of the discharge environment.

Each valve is supplied with a manufacturer’s Typical Test Report containing the set and hydraulic test pressure. Material certification to EN 10204 3.1 is available on request. The product documentation also records CE/PED and pressure-equipment-category information, seat-tightness testing to ASME/API Standard 527-1992, the applicable TÜV approvals and Lloyd’s Register type approval. The exact certificate and marking requirements still need to be confirmed for the destination market and the specified valve.

Pressure, temperature and relieving conditions

The SV604 technical sheet gives a minimum set pressure of 0.2 bar g, a maximum temperature of 400 °C and a minimum temperature of -10 °C. These are boundary values within the documented selection envelope, not a blanket permission to combine the maximum temperature with every pressure, size, connection or spring. The PN40 inlet graph identifies a region where the product must not be used and a region where a tungsten-alloy spring is required. The graph must be read with the selected set pressure and the actual fluid.

For PN40 SV604 configurations, the maximum set-pressure entry varies with the inlet/outlet size pair and with saturated steam, air or water. The technical tables show the corresponding limits and capacity data. Steam rated capacity is calculated at 5% overpressure. The stated overpressure for liquids and gas is 10%; the blowdown limit is 10% for steam and gas and 20% for liquids. Superimposed backpressure is limited to 10% of set pressure. These relationships are important because a valve that is correctly sized for one relieving medium or backpressure condition cannot be assumed to have the same duty for another.

Capacity selection requires the required relieving load, set pressure, inlet and outlet size, fluid state, temperature, allowable overpressure and backpressure. The technical information section provides the dry saturated steam, air and water tables, plus the flow-area and coefficient data used with the documented calculation method. The maximum inlet cold hydraulic test pressure is 60 bar g; it is a test boundary and should not be treated as the normal operating pressure.

Installation and system integration

Install the valve with its main axis vertical and the centre line of the spring housing vertically above the valve. The inlet connection should be as short as practicable and no smaller than the valve inlet. There must be no intervening valve or fitting that could isolate the safety device from the protected system. The outlet pipe should be at least as large as the valve outlet, use suitable long-radius fittings, and discharge to a location where hot, pressurised fluid and noise cannot injure people or damage equipment.

The discharge pipe needs independent support so its weight and thermal movement do not load the valve. Each safety valve should have its own unrestricted discharge pipe. Where condensate can collect, the body drain connection should be routed to a safe drain. On steam service, a small-bore drain is required at a suitable low point when the outlet rises. Body lagging should be limited as instructed in the installation guide, and the surface must be treated as hot during operation.

Inlet pressure loss is a key damage-prevention check. The installation guide limits inlet pressure loss to no more than 3% of the pressure differential between set pressure and superimposed backpressure while discharging, and recommends positioning the valve 8–10 pipe diameters downstream of converging, diverging fittings or bends. Chattering or hammering can reduce capacity, damage seating faces and leave the valve leaking after the system returns to normal pressure.

Commissioning, testing and maintenance

Before fitting, confirm the name-plate information, set pressure, fluid, material suitability and installation direction. Blow through the pipework before installation so foreign matter cannot damage the seat. Remove transport protection and easing-lever restraints only after the installation is ready. Work on the valve requires competent, trained personnel, suitable isolation and safe venting; the internal spring must be released before dismantling.

During commissioning, check the inlet and outlet connections for leaks, raise system pressure in a controlled manner, verify operation at the required set pressure and confirm the applicable overpressure limit. Reduce pressure to the normal operating condition and check that the valve reseats. Testing should form part of a documented procedure at least every 12 months unless the application, system conditions or responsible authority require a different interval. An easing lever must only be operated by hand when system pressure is at least 85% of set pressure; tools or extensions must not be used.

Planned maintenance is essential for a safety device. The installation guide recommends internal inspection no later than five years, or at an interval agreed with the insurance company, with overhaul, testing, resetting and sealing carried out by the manufacturer or an approved specialist. Disc and skirt assemblies are non-serviceable. Do not repair or rectify them in the field; damaged assemblies must be replaced or handled by an approved repair specialist. Heat, stored pressure, discharge noise and any process contamination must be controlled before inspection or removal.

How to select an SV604

1. Define the protected equipment, design pressure, normal operating pressure, relieving medium, temperature range and required relieving load.

2. Choose the inlet/outlet size pair from the documented DN20–DN150 range and confirm the flange standards and pressure route.

3. Set the valve within the protected equipment limit while leaving enough operating-pressure margin for stable reseating.

4. Check the SV604 PN40 pressure/temperature graph, overpressure, blowdown and backpressure limits for the actual service.

5. Specify bonnet, cap, easing lever and spring configuration, including the open-bonnet requirement for a tungsten-alloy spring.

6. Confirm discharge piping, drains, supports, certification, local approvals and the required test documentation before ordering.

Use the safety valve range as the category-level route when the protected-equipment duty or connection requirement indicates that a different product family should be evaluated. For a Spirax Sarco SV604 enquiry, provide the exact size, connection, set pressure, fluid, temperature, relieving load and bonnet/spring configuration so the selection can be checked against the official technical and installation documents.

Documented information for the project file

The technical information section that follows carries the model boundaries, pressure/temperature limits, capacity tables, material schedule, dimensions and selection guide from TI-S13-27, CMGT Issue 19. The installation section carries the safety information, handling, fitting, damage-prevention, commissioning, testing, setting and maintenance requirements from IM-P317-01, CTLS Issue 13. Together they give the engineer a traceable starting point; final sizing, conformity and installation approval remain responsibilities of the competent designer and installer.