The device and principle of operation of the thermostatic valve


Mod­ern ener­gy sources have a fair­ly high cost, so every own­er of an apart­ment or a coun­try house is think­ing about how to make the heat­ing sys­tem more ener­gy effi­cient. Not so long ago, users did not have the oppor­tu­ni­ty to reg­u­late the sup­ply of heat to the room, there­by sav­ing con­sump­tion. The con­struc­tion indus­try is con­stant­ly improv­ing, and spe­cial devices are now avail­able — ther­mo­sta­t­ic valves. These are sim­ple, reli­able and inex­pen­sive ele­ments that allow you to main­tain the desired air tem­per­a­ture in the room and reg­u­late ener­gy con­sump­tion. The prin­ci­ple of oper­a­tion, types and fea­tures of the ther­mo­sta­t­ic valve will be dis­cussed below.

ther­mo­sta­t­ic valve

Purpose of the device

It hap­pens that in the premis­es, in addi­tion to radi­a­tors, oth­er heat sources act — house­hold appli­ances, gas or elec­tric stoves, and so on. On sun­ny days, the tem­per­a­ture ris­es and the house becomes warmer than usu­al.

Impor­tant! The task of the ther­mo­sta­t­ic valve installed on the radi­a­tor is auto­mat­ic tem­per­a­ture con­trol, dur­ing which it takes into account tem­per­a­ture fluc­tu­a­tions in the room at a height of up to 2 meters.

The ther­mo­sta­t­ic valve for radi­a­tors ensures the reli­a­bil­i­ty of ther­mal equip­ment. By includ­ing it in the heat­ing sys­tem, a com­fort­able and opti­mal room tem­per­a­ture is achieved and, at the same time, mon­ey spent on ener­gy con­sump­tion is saved. The valve sta­bi­lizes the oper­a­tion of the heat­ing sys­tem if the pres­sure drops or dis­ap­pears in it.



There is a wide vari­ety of mod­els of such valves, but their design is sim­i­lar.

Manda­to­ry lay­out includes the fol­low­ing ele­ments:

  • body, usu­al­ly made of brass;
  • a mix­er used as a direc­tion­al reg­u­la­tor;
  • con­trol lever;
  • oth­er small parts in the form of seals, nuts and so on.

The valve body has 2 inlets and 1 out­let. A liq­uid of dif­fer­ent tem­per­a­tures enters through the inlets, and through the out­let it exits, already heat­ed to the required tem­per­a­ture. In the inner part of the hous­ing there is a mix­er that reg­u­lates the direc­tion. This ele­ment, depend­ing on the valve mod­el, func­tions dif­fer­ent­ly. A sim­ple option — a spring lock­ing ele­ment is installed in the design, which reacts to tem­per­a­ture, and, accord­ing­ly, pres­sure. If the spring ten­sion increas­es, the out­let tem­per­a­ture decreas­es.

The con­trol knob is need­ed in order to set a spe­cif­ic posi­tion of the valve. With its help, the spring stiff­ness is set and the posi­tion of the lock­ing part is adjust­ed.

Valve design

Principle of operation


In the body of the device, in the front and right pipes, the coolant cir­cu­lates until its tem­per­a­ture reach­es the set val­ue. The ther­mo­sta­t­ic valve is installed in order to main­tain a giv­en out­let tem­per­a­ture by mix­ing cold or hot water into the liq­uid. If the para­me­ters do not con­verge, then the exter­nal dri­ve of the device acts on the rod. When it starts to move, all 3 chan­nels open in the body. And, as soon as the tem­per­a­ture para­me­ters sta­bi­lize, the front inlet pipe is closed.

There is a con­sid­er­able vari­ety of ther­mo­sta­t­ic valves and three-way valves. One of the vari­eties is sim­i­lar to a ball valve. In this mod­el, the changeover valve con­sists of a recessed ball rather than a cone seat. To redis­trib­ute the coolant, the dri­ve acts on the rod with the fixed ball, rotat­ing it. Such valves have a low through­put, there­fore they are used only in domes­tic heat­ing sys­tems. In short, a ther­mo­sta­t­ic valve sets the required water tem­per­a­ture.

What are the types of valves

Design fea­tures are not the only thing that dis­tin­guish­es mod­ern ther­mo­sta­t­ic valves. These ele­ments are made of var­i­ous mate­ri­als, have dif­fer­ent diam­e­ters and con­nec­tion meth­ods. Let’s get acquaint­ed with the main types.

Production material

The main con­di­tion is that the mate­r­i­al from which the valve is made must be resis­tant to mechan­i­cal stress and cor­ro­sion. This is explained by the fact that the ele­ment is in con­stant con­tact with the liq­uid — the coolant.

The mate­r­i­al from which the valve is made deter­mines the per­for­mance and tech­ni­cal char­ac­ter­is­tics of the prod­uct. It is rec­om­mend­ed that the valve be made of cop­per, brass or cast iron. Cop­per options are expen­sive, but last a long time. Brass sam­ples also have a long ser­vice life and do not cause dif­fi­cul­ties dur­ing oper­a­tion. In gen­er­al, in order to make the right choice, it is bet­ter to seek advice from the com­pa­ny’s spe­cial­ists who will set up the heat­ing sys­tem.


Control method


Accord­ing to this para­me­ter, devices of 2 types are dis­tin­guished:

  • elec­tri­cal;
  • man­u­al.

Often a man­u­al ver­sion is installed, visu­al­ly sim­i­lar to an ordi­nary ball valve. More mod­ern mod­els with elec­tric fill­ing are pop­u­lar in pri­vate homes — they are con­trolled auto­mat­i­cal­ly, dis­trib­ut­ing heat through­out the room. Adjust­ing the ther­mo­sta­t­ic valve is sim­ple — the user sets the desired heat­ing tem­per­a­ture for each room and the device sup­plies the work­ing flu­id to the heater. If desired, such a sys­tem is com­bined with a “warm floor”, but it is nec­es­sary to think over a way to cre­ate a pro­tec­tive coat­ing for pipes.

Wiring diagram

Hav­ing fig­ured out what the valve con­sists of and on what prin­ci­ple it func­tions, we will con­sid­er var­i­ous schemes for con­nect­ing it. It all depends on the pur­pose for which the ther­mo­sta­t­ic bal­anc­ing valve is installed.

What is a valve for?

  1. Pro­tects the sol­id fuel boil­er from the effects of con­den­sate and tem­per­a­ture shock, which hap­pens as a result of a sud­den pow­er out­age.
  2. So that the coolant cir­cu­lat­ing in the “warm floor” sys­tem does not warm up above +45 degrees Cel­sius.
  3. Main­tains the required tem­per­a­ture of the coolant in the heat­ing sys­tem, and hence the pres­sure in the pipeline.

To pro­tect the ther­mal unit oper­at­ing on sol­id fuel, it is not allowed that cooled water from the heat­ing sys­tem enters its cir­cuit. To do this, the boil­er is con­nect­ed accord­ing to a spe­cial scheme, which includes not only a mix­ing valve, but also a bypass. The oper­a­tion of the cir­cuit is as fol­lows: the coolant will cir­cu­late in a small cir­cle through the bypass until the heat gen­er­a­tor warms up. When the tem­per­a­ture reach­es +50–55 degrees Cel­sius, the valve will start to open, mix­ing cold water from the sys­tem. When the boil­er reach­es oper­at­ing tem­per­a­ture, the bypass is closed and all flow begins to flow through the radi­a­tors.

Sim­i­lar func­tions and when con­nect­ed to the “warm floor” sys­tem. The pump cir­cu­lates the coolant in the cir­cuit until it cools down. As soon as this hap­pens, the sen­sor and valve are acti­vat­ed and hot water from the boil­er will be added to the sys­tem.

This impor­tant detail is also used when tying a sol­id fuel boil­er and a buffer tank, which plays the role of a heat accu­mu­la­tor. For its effec­tive heat­ing, the tem­per­a­ture of the coolant should reach + 70–85 degrees Cel­sius, which is high­er than the norm for radi­a­tors. The ther­mo­sta­t­ic valve is used to low­er the tem­per­a­ture. To do this, it is installed behind the tank, paired with pump­ing equip­ment.

Note! When installing a mix­ing valve, the pump should be locat­ed on the side where the always open branch pipe of the tap is locat­ed.


Often, ther­mo­sta­t­ic changeover valves are installed in large cot­tages with a com­plex heat­ing sys­tem, with a hydraulic arrow and a dis­tri­b­u­tion man­i­fold. Each cir­cuit in such a sit­u­a­tion requires a cer­tain tem­per­a­ture. The high­est heat val­ue is need­ed by the boil­er, there­fore, the reg­u­lat­ing tem­per­a­ture is not sup­plied to it. But for the rest of the con­sumers, a not so hot coolant is sup­plied, so they are con­nect­ed through ther­mo­sta­t­ic valves.

Valve type

Installation Features


Heat­ing sys­tems are assem­bled accord­ing to var­i­ous schemes, which will deter­mine the loca­tion of hot water pipes, plugs and con­trol valves. Before start­ing the instal­la­tion, you need to shut off the coolant sup­ply to the radi­a­tor and drain the remain­ing water.

With a sin­gle-pipe heat­ing sys­tem, hot water cir­cu­lates through one pipe, and heat­ing devices are con­nect­ed in series. The coolant is sup­plied to the radi­a­tor through a spe­cial pipe installed on top. In the cir­cuit, it pass­es through the bat­tery and exits on the oth­er side, redi­rect­ing to the high­way. With this con­nec­tion, the ther­mo­stat is mount­ed on a bypass con­nect­ing the direct and return pipes of the heat­ing device. And even if the valve is closed, hot water will still con­tin­ue to move. Ther­mo­stat fail­ure can occur if bypass­es are not installed under the pipes. If one bat­tery is dis­con­nect­ed, then not only the valve will fail, but the entire heat­ing sys­tem will fail.

In two-pipe sys­tems, things are dif­fer­ent, since in it the coolant is sup­plied through one pipe, and it is dis­charged through the oth­er. A jumper, that is, a bypass, is not required in this sit­u­a­tion, so a ther­mo­sta­t­ic valve is installed on the sup­ply pipe. The con­trol valve is also effec­tive in indi­vid­ual heat­ing sys­tems. It is also rel­e­vant for cen­tral­ized net­works, but tak­ing into account the fact that a hot water meter is pro­vid­ed.

Valve installed in the heat­ing sys­tem

Before you start set­ting the ther­mo­stat, you first need to iso­late the room from heat loss. To do this, close all doors and win­dows. Next, the valve is set to max­i­mum heat out­put and the heat­ing is turned on, after which the tem­per­a­ture in the room is mea­sured. After its increase by 5 degrees, the valve is closed. Now you need to wait a bit and slow­ly open the reg­u­la­tor until the water comes out. This posi­tion should be remem­bered.


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