Main Types of Safety Valves and Their Applications

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Dur­ing the oper­a­tion of any sys­tem in pipelines, due to a mal­func­tion, high pres­sure can occur, which can lead to the destruc­tion of equip­ment. To pro­tect the units, a safe­ty valve is installed in the sys­tem, which, if the pres­sure in the pipelines ris­es above the nom­i­nal val­ue, releas­es the excess work­ing medi­um, and the nom­i­nal pres­sure is restored in the sys­tem.

The principle of operation of safety valves

The high pres­sure safe­ty device is installed in pipelines and ves­sels under pres­sure. Depend­ing on the pur­pose, the design of safe­ty ele­ments may be dif­fer­ent, but the scheme and prin­ci­ple of oper­a­tion are the same for all.

Dur­ing nor­mal oper­a­tion of the equip­ment, the seat is closed by the spring mech­a­nism and has no effect on the sys­tem. The valve set­ting pres­sure is equal to the oper­at­ing pres­sure in the sys­tem. When the pres­sure in the pipelines exceeds the force of the spring ele­ment clos­ing the hole, the seat will open and the con­duc­tive medi­um will be eject­ed. As a result, the pres­sure will drop and the seat will close again.

Relief valve dia­gram

The work­ing medi­um can be dif­fer­ent, water, steam, gaseous frac­tions, lubri­cat­ing and hydraulic oils and petro­le­um prod­ucts. There­fore, excess pres­sure can also be dis­charged to the atmos­phere, for exam­ple, steam, air, water, or back to the drain line for aggres­sive mate­ri­als.

The safe­ty valve begins to open slight­ly to relieve pres­sure at a pres­sure of 3% below the nom­i­nal. The dis­charge of the work­ing medi­um is ini­tial­ly small, but if this is not enough and the pres­sure increas­es, then the sad­dle will open access to the drain at 110–115% of the work­ing one.

After the pres­sure drops, the seat will block access, and the sys­tem will con­tin­ue to work in nor­mal mode.

Application of safety devices

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To ensure safe oper­a­tion, the safe­ty fit­ting is an essen­tial ele­ment of any pres­sur­ized sys­tem.

Depend­ing on the pur­pose, they can be installed in the fol­low­ing places:

  1. Hot water sup­ply and heat­ing. The safe­ty valve for the heat­ing sys­tem is installed on the pipelines after the sup­ply pump. Since hot water is cor­ro­sive, the dis­charge must be direct­ed to a safe place, usu­al­ly a sew­er. At high costs, the num­ber of units can reach up to 2 or more.
  2. A plumb­ing fit­ting for a cold water pipeline is installed in drink­ing water sup­ply pipelines. Dis­charge is made direct­ly to the ground.

    Plumb­ing fit­ting for water sup­ply
  3. Hydraulic sys­tem. Hydraulic oils are used as the work­ing flu­id. The hydraulic sys­tem serves to dri­ve the work­ing mech­a­nisms: hydraulic motors, hydraulic cylin­ders. The safe­ty fit­ting is installed on pipes, or may be part of a pump or con­trol valve. The oil is dis­charged into the drain line.
  4. Gas sup­ply pipelines. Increas­ing the pres­sure in the pipes can lead to an emer­gency — this is the sep­a­ra­tion of the flame from the burn­ers, the accu­mu­la­tion of excess gas and an explo­sion in the room. There­fore, the fit­tings are installed imme­di­ate­ly after the pres­sure reg­u­la­tor, and the dis­charge is made to the atmos­phere.
  5. Air sys­tem, com­pres­sors. The safe­ty device is installed in the com­pres­sor cas­ing and dis­charged to the atmos­phere.
Com­pres­sor Safe­ty Fit­ting

Types of protective mechanisms

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In indus­try, var­i­ous designs of pipe pro­tec­tion devices are used, depend­ing on their instal­la­tion loca­tion and the con­duc­tive medi­um. These can be spring, lever, diaphragm, two-posi­tion and oth­er types of safe­ty valves used.

Let us con­sid­er in more detail their device and prin­ci­ple of oper­a­tion.

Spring safety valve

The most wide­ly used safe­ty valve, espe­cial­ly for heat­ing sys­tems. Its main advan­tages are sim­plic­i­ty of design and the abil­i­ty to eas­i­ly adjust to the work­ing pres­sure in the sys­tem. There are the fol­low­ing types of pro­tec­tive spring mech­a­nisms:

  • direct action — the device is trig­gered by direct expo­sure to the work­ing envi­ron­ment;
  • indi­rect action — the over­pres­sure is dis­charged by an exter­nal con­trol, for exam­ple, an elec­tri­cal sig­nal;
  • two-posi­tion units — the open­ing of the fit­ting occurs imme­di­ate­ly abrupt­ly at full speed, after the pres­sure is released, the fit­ting clos­es abrupt­ly, which can cause self-oscil­la­tions of the seat and vibra­tion of the mech­a­nism.
Two Posi­tion Fit­ting

Lever type safety mechanism

The mech­a­nism of this fit­ting con­sists of a lever con­nect­ed to a spool that clos­es the out­let port. A load is sus­pend­ed on the lever, and, depend­ing on the weight of the load and the place of attach­ment on the lever, the mech­a­nism set­ting is adjust­ed.

The load is fixed on the lever against acci­den­tal dis­place­ment and set­ting changes. The dis­ad­van­tage of this design is its bulk­i­ness, there­fore, the use of such mech­a­nisms is car­ried out in sys­tems with a large pipe diam­e­ter, more than 50 mm.

Lever type safe­ty device

Diaphragm safety valve

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The main ele­ment of this design is the mem­brane. The prin­ci­ple of oper­a­tion is that when an emer­gency pres­sure occurs in the pipes, the mem­brane breaks and the work­ing medi­um is dis­charged. Mem­brane devices are easy to man­u­fac­ture, her­met­i­cal­ly sealed and respond quick­ly.

Impor­tant! They have a sig­nif­i­cant draw­back, after each oper­a­tion the mem­brane must be changed to a new one. There­fore, a con­ven­tion­al fit­ting is always placed next to such a device.

Depend­ing on the design, such devices can be with a burst­ing disc and with a slam­ming disc:

  1. Rup­ture disc mech­a­nisms are used in sys­tems with liq­uid and gaseous work­ing media. The shape of the mem­brane is flat or dome-shaped, with a sharp change in pres­sure above the work­ing device, the device is trig­gered and the mem­brane is destroyed.
  2. Flap­ping diaphragm mech­a­nisms are used most often in sys­tems with a gaseous work­ing medi­um. The mem­brane is made of rub­ber fab­ric and pro­tects the pipes from both pres­sure buildup and dan­ger­ous pres­sure drops. To do this, knives are locat­ed above and below the mem­brane. When the pres­sure changes, the mem­brane bends, and when, with a sharp drop in the sys­tem, it touch­es the knives, the shell is cut. In this case, depend­ing on the mag­ni­tude of the pres­sure, either a dis­charge or a replen­ish­ment from an addi­tion­al tank occurs.
Safe­ty diaphragm device

Installation and installation

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To ensure the safe oper­a­tion of gas and water pipelines, when installing pro­tec­tive units, it is rec­om­mend­ed to com­ply with the fol­low­ing require­ments:

  1. Shut-off valves and fil­ters must not be installed on pipes suit­able for the pro­tec­tive mech­a­nism and pres­sure relief pipelines.
  2. The axis of the spring fit­ting must be installed ver­ti­cal­ly. The unit must be freely acces­si­ble for replace­ment and adjust­ment.
  3. The lever-type safe­ty lever must be hor­i­zon­tal when installed.
  4. A pres­sure gauge must be installed in front of the fit­ting to con­trol the pres­sure.

    Instal­la­tion of a pres­sure gauge on the pipeline
  5. Depend­ing on the work­ing medi­um, the dis­charge pipe can be direct­ed: to the atmos­phere for steam and gaseous non-aggres­sive media. For hot water, the drain must be direct­ed to a spe­cial con­tain­er, or back into the sys­tem. If there is an aggres­sive medi­um in the pipes, then the dis­charge should only be drained into a closed tank.
  6. The length of the pipe from the equip­ment to the instal­la­tion of the pro­tec­tive unit must be kept to a min­i­mum. In this sec­tion, it is not allowed to con­nect branch­es for the selec­tion of the work­ing medi­um.
  7. The safe­ty valve for the heat­ing sys­tem can be installed in sev­er­al places on the pipeline, while the flow rate of the work­ing medi­um through the pipeline must be 1.25 times greater than the total flow rate of the installed devices.
    Instal­la­tion of equip­ment in the boil­er room

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  8. Before putting the sys­tem into oper­a­tion, it is imper­a­tive to check the cor­rect set­ting of the safe­ty valve, as well as its abil­i­ty to return to its orig­i­nal posi­tion and ensure tight­ness.

Exploitation

The dura­bil­i­ty of the pro­tec­tive mech­a­nisms depends on com­pli­ance with all con­di­tions of tech­ni­cal oper­a­tion. Dur­ing the oper­a­tion of the pro­tec­tive unit due to wear of the main parts, the fol­low­ing defects may occur:

  1. Seat leak­age. The defect may occur as a result of the ingress of met­al chips and the pres­ence of scratch­es on the sad­dle. The defect is elim­i­nat­ed by grind­ing the seat or replac­ing it with a sim­i­lar fit­ting.
  2. Under­stat­ed open­ing pres­sure of the device due to the loss of its elas­tic prop­er­ties by the valve spring or mis­ad­just­ment of the set­ting. To elim­i­nate the fail­ure, it is nec­es­sary to replace the spring or the fit­ting itself, adjust the pres­sure, check in oper­a­tion and put a seal.
  3. If it is nec­es­sary to replace the unit for repair, then a plug or valve can­not be tem­porar­i­ly placed in its place. It is nec­es­sary, for the safe­ty of the object, to first select a valve with exact­ly the same char­ac­ter­is­tics, and only install it instead of the removed one.
  4. If there is a pul­sa­tion dur­ing oper­a­tion, rapid open­ing and clos­ing of the shut­ter of the device, then such a defect can cause unwant­ed vibra­tion of the pipelines, which can lead to their defor­ma­tion. The rea­son may be a mis­match between the dimen­sions of the sec­tions of the main pipeline and the pipeline con­nect­ed to the unit. To elim­i­nate the defect, it is nec­es­sary to install pipes of the same cross sec­tion dur­ing instal­la­tion.

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