The line between the expansion tank and boiler should not be blocked by a normal backflow preventer (BFP). But some BFP are made for that location since they do have a tiny hole which is allowing a tiny back flow during heating up.

First select a size, then the appropriate pressure rating or pressure group. Now a spring range by clicking on the round circles. Then select the proper material for the body #8 and poppet #7 which are the only wetted materials in this valve. Next, select the proper piston seal material #9, which must also be suitable for the media used. The more elastic Buna and Viton & Epdm seals tend to create less of a piston drag than the harder Teflon (PTFE) seal. The softer elastomeric seals produce a much closer band between crack and reseating pressures. Normally viton will handle most solvents, oils and chemicals and can handle most media between 300F to 400 deg F. Next select the Spring chamber #3, spring hardware #1 & #2. The adjusting spring #5 is normally supplied in a chrome silicon steel which is completely protected inside the spring chamber and is not wetted or exposed to the flow media. These are all isolated (non-wetted) from the fluid media and should be selected based on the external environment the valve is exposed to. The carbon steel spring chamber, when selected, is painted on the exterior and interior to withstand normal atmospheric corrosion. After the customized selection is made, click to continue and instructions will be provided to either print or save the selection or to proceed with ordering the item on line. Printing the selection will not commit one to ordering the items selected. Should you have any questions on the product capability or product options, or are having difficulty in making the pricing selections or ordering, please contact us by e-mail or phone between 9AM-5PM Eastern time, Monday-Friday.

These valves do not carry the Canadian CRN or ASME approval stamp and should not be applied where this requirement must be met. However, the valves generally meet or exceed ASME design criteria with wall thicknesses that are much heavier than the minimums required. For an additional charge, valves can be ordered with material certs and with a certified hydro-test certificate and other tests to meet special documentation and acceptance requirements.

Safety relief valve should only be used selectively where the materials chosen are compatible with the fluid used and will not cause corrosive buildup, crystallization or solidification in the close clearances between the piston and body bore, which could keep the poppet from opening freely. Use only clean, strained (#20 mesh min), or filtered liquids or gases so that the  valve can operate without buildup of debris or solid matter which can cause the valve to malfunction. A basket strainer or high-pressure filter with the appropriate material and pressure rating can be purchased from Stra-Val. Avoid locating the valve where freezing can occur, and if unavoidable, take precautions to insulate or heat wrap valve and piping to keep from freezing.

Here is some info for installers/engineers, allow some seconds for translation. https://www-bosy--online-de.translate.goog/ausdehnungsgefaesse.htm?_x_tr_sch=http&_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp

BFP can be very small inlets, f.e. of the size of a coin that fits into pump/tube connections, i.e. it is not always visible from outside, if/where a BFP is installed:

https://www-bosy--online-de.translate.goog/Schwerkraftbremse.htm?_x_tr_sch=http&_x_tr_sl=de&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp

If that hole is blocked, the pressure can not be compensated by the expansion tank but must be released by the pressure relief valve.

Use these valves for emergency relief where pressures must be relieved quickly to reduce damage that could result from overpressure in a system. Where the overpressure needs to be controlled more gradually ,such as in back pressure or pump bypass applications use our Back-pressure/Bypass valves which will reduce the probability of pressure spikes that often occur when relief valves are selected for pressure control applications. Standard metal seated valves meet ANSI/FCI Class IV seat leakage standards (0.01% of rated valve capacity,  not bubble tight).

You may have a defective boiler feed water pressure regulator. (Looks like this.) This device takes water from your plumbing system and feeds it into the boiler until the pressure in the boiler reaches a certain level, typically 12 PSI. Then it stops adding water unless the pressure again drops below 12 PSI for any reason, such as a leak or the intentionally draining of some water. When the boiler heats up, expansion takes place and the water pressure rises a bit above 12 PSI. This excess pressure is absorbed by the expansion tank so the final pressure of the hot boiler may go up to 15-20 PSI typically, which is below the usual 30 PSI setpoint of the pressure relief valve.

Boilerpressure relief valve replacement

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Note: Dimensions are approximate and are subject to change without notice. Request certified dimensions before final product installation.

Although the valve is typically installed in the position illustrated, it can operate in any position or orientation, vertical horizontal, etc as long as it can be easily accessed for making adjustments.

Prv for boilerdiagram

These valves are not equipped with a manual lever release. However, manual override is accomplished by first unlocking the spring lock nut to the adjusting screw and backing it out enough to open the poppet to release pressure, and then repositioning it to its original preset locked condition without losing the original set pressure. This procedure is recommended periodically to flush the seat and to check for proper opening of the valve piston.

Boilerpressure relief valve dripping

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Some regulators include a backflow preventer and some use a separate backflow preventer that is installed between the regulator and the boiler. The backflow preventer prevents boiler water from backing up into your household plumbing and potentially poisoning you.

5.) As you click on each option, you will see the subtotal change. You must click on all available options before proceeding to the next step.

The Vetus anti syphon device helps to prevent cooling water from siphoning back into the exhaust and ultimately into the engine when it is off.

4.) By placing your mouse over each option you will see a pop up display with helpful information including temperature limits for that material or option

A problem I had (twice) with a boiler, was a pin-hole leak in the coil for the domestic HW supply. It let curb pressure cold water into the boiler which exceeded the relief valve. Eventually had to buy a better quality coil for the water type. A diagnostic would be be shut off that water feed and see if the problem abates.

Series LF007 Double Check Valve Backflow Preventer are designed to protect drinking water supplies from dangerous cross-connections.

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Recently my boiler is leaking periodically through the pressure relief valve. I replaced with a new pressure relief valve. Still leaking so I hired a plumber he said my expansion tank is filled with water and it’s most likely the issue. I paid and had the expansion tank changed. Few hours later, it leaks again and now the condensate pipe has a small leak too. Every time it leaks, I noticed the pressure reading is very high up to 40 psi. I am completely lost now. What’s going on with my boiler? My plumber stated if the issue is not fixed, next will be changing the backflow preventer which will cost me about 500. I just want to know if this makes sense. I tried to research on the Internet finding relevant information, but couldn’t find the connection between backflow preventer and high pressure water leak.

Your plumber may be planning to replace the feed water regulator and the backflow preventer at the same time, which should solve the problem. Or you could tackle this yourself if you're able.

Boilerpressure relief valve discharge pipe

Prv for boilerreplacement

6.) Click on the large "Continue" button to apply quantity and resale discounts, Print, E-mail the quote to yourself, or to Order.  You  will be given a  resale discount code if you are an eligible reseller or OEM.

If the regulator is faulty, it may be allowing water to continue to flow slowly into your boiler, raising the boiler pressure until it reaches 30-40 psi. At that point, the pressure relief valve would start dripping.

Scroll down below to select the valve size, spring range, material options in the customized pricing and ordering section indicated by the red arrows. You have the ability to customize your valve choices by selecting the wetted and nonwetted materials, and choice of seat materials to suit your shutoff requirements, using the softer seats for improved shutoff, particularly for air or gas applications where they are available at the lower pressures. Once these selections are made a price quote can be generated and printed directly to your computer or immediately e-mailed to you. When ordering don't forget to state your desired relief set pressure if you expect the valve to relieve at only one pressure. This pressure will be engraved on the valve body. If the set pressure is not specified, the valve will be set at or below the stated spring range as selected for the order and no set pressure will be stamped on the nameplate.

Prv for boilerinstallation

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Rotork pressure relief valves provide an alternative flow path for liquids and gases when there is an overpressure.

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How to useprv for boiler

This is a poppet and spring type relief valve where the spring constantly opposes the pressure acting against the poppet which seals off the inlet port from the outlet port at the valve seat. The desired set pressure or relief is achieved by compressing the spring until the spring force is adequate to balance the pressure force acting against the poppet. When the inlet pressure exceeds the set pressure, the poppet will open to relieve the excess pressure. The valve will operate in a vertical orientation as illustrated, horizontal, or any other orientation.

The water pressure regulator works on the principle of pressure reduction. It is preferably for use in the provided water systems. The pressure regulator ...