Injection valve for chemical dosing (the quill and check valve at the dosing point, and the back-pressure valve that stops siphoning)
The valve where a dosing line enters the process pipe · injection quills that reach the pipe centreline, a spring-loaded check against back-siphoning, insertion length by pipe size, body material against pressure and temperature, and a back-pressure valve at the dosing point when the line has no downstream pressure
A dosing pump's discharge line ends at an injection valve on the process pipe. It has three jobs: deliver the chemical into the moving stream rather than along the pipe wall, stop process fluid flowing back up the dosing line, and stop the chemical line siphoning into the process when the pump is idle. Quill length, check valve, materials and the valve arrangement around it are specified together.
Injection valves and injection quills at chemical dosing points, with their check valves and the back-pressure or anti-siphon valves near them. Metering pumps are covered on the Metering pump page; packaged dosing skids on the Chemical dosing pump skid (packaged duty/standby dosing system for water treatment) page; CIP dosing on the CIP chemical dosing unit for detergent and sanitizer strength control page; beverage additive injection pumps on the Hygienic precision metering pump assembly for injecting flavours and additives into a beverage stream page; fertigation injectors on the Liquid fertiliser injection system (fertigation injector) page.
CNFX editorial research · Sources checked October 13, 2026 · 2 sources
Primary Fluid Systems' injection quill instructions (Rev. 3, 10/12) describe the quill as "ideal for the injection of chemicals into the center stream of a process pipeline" for a more homogeneous mix, with a built-in spring-loaded check "to help prevent back siphoning". A 3 in. injection length suits 4–6 in. pipe and a 5 in. length 8–10 in. pipe; for pipe below 4 in. the quill can be trimmed so its tip sits on the pipe centreline. [1]
The quill is installed with the stamped arrow facing downstream, so the angled face points into the stream; an isolation valve behind it is recommended for maintenance; and a quill ordered without a spring should sit at the 6 o'clock position to help the check seat. [1]
The same document describes the check both as "a built in stainless steel spring-loaded check" and as having "a Hastelloy C spring" as standard, with 316 stainless and titanium springs available; confirm the spring material against the chemical. Its pressure ratings are based on 73 °F (23 °C). [1]
PFS quill body (3 in. and 5 in.)
Max. pressure
Max. temperature
Ball / spring
PVC
150 psig
140 °F (60 °C)
Ceramic / Hastelloy C
CPVC
150 psig
210 °F (98 °C)
Ceramic / Hastelloy C
PP
150 psig
195 °F (90 °C)
Ceramic / Hastelloy C
PVDF
150 psig
260 °F (125 °C)
Ceramic / Hastelloy C
316 stainless
3000 psig
500 °F (260 °C)
Ceramic / Hastelloy C
Hastelloy C
3000 psig
500 °F (260 °C)
Ceramic / Hastelloy C
Give the supplier the chemical and its concentration, process pipe size and pressure, process temperature and flow, and ask for quill length, body, ball and spring materials, and the check valve's opening pressure.
02
Back-pressure and anti-siphon valve near the injection point
Walchem's back pressure and pressure relief valve manual (180280.E, 12/2012) describes its diaphragm back pressure valves as giving a constant discharge head pressure to a chemical feed pump and acting "as an anti-siphon valve", adjustable from 10 to 150 psi and factory set at 50 psi. [2]
Walchem states that the back pressure valve "can be installed anywhere in the discharge line, provided there is some downstream pressure at the dosage point", and that "If there is no downstream pressure the back pressure valve should be installed at the dosage point to prevent siphoning and drainage of the chemical line." Its installation diagram shows the injection valve, back-pressure/anti-siphon valve, pressure relief valve, pulsation dampener, calibration cylinder and Y-strainer around the pump. [2]
For pulsation dampeners used with the back pressure valve, Walchem gives sizing of 12 to 15 times the dosage volume of the pump head for non-diaphragm types. [2]
State whether the injection point is ever at or below atmospheric pressure, or lower than the chemical tank, and ask where the back-pressure or anti-siphon valve will be fitted and at what setting.
03
Injection valve details
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why use an injection quill rather than a tee?
Primary Fluid Systems says the quill injects into the centre stream for a more homogeneous mix. [1]
How long should the quill be?
In PFS's range, 3 in. for 4–6 in. pipe and 5 in. for 8–10 in.; trimmed for smaller pipe so the tip is on the centreline. [1]
What pressure can a PVC quill take?
150 psig at 73 °F in PFS's table, against 3000 psig for 316 stainless. [1]
Where should the anti-siphon valve go?
At the dosage point when there is no downstream pressure, according to Walchem. [2]
Sources and what still needs a direct check
Sources checked 2026-10-13. Primary Fluid Systems publishes its metering pump injection quill instructions (copy hosted by distributor Trility); Walchem (Iwaki America) publishes its back pressure and pressure relief valve manual.
