Kitchen Gas Stove Valve

My gas pressure is 3 to 5 PSI.

My gas kitchen stove does not modulate. It is a simple thermocouple/gas valve operation - below setpoint = on, at setpoint = off.

The gas valve opens when I turn the oven knob to 350 degrees.

Once 350 degrees is sensed by the thermocouple the gas valve closes.

After a degree or two drop sensed by the thermocouple the gas valve opens again.

This cycle continues until I turn the oven knob to the off position.

Here is a site that explains modulating fuel scenarios:

http://www.camus-hydronics.com/Service_Manuals/MicoFlame_Modulating_IOS_Manual%20(Rev%2000).pdf

Thank you very much for you input. Is it the case that most gas valves do not modulate. What about the burners, I am sure you have the modulate the kitchen stove burners to adjust the flame size.

Yes, you "modulate" the stove top burners by rotating the gas supply knobs by hand.

What kind of valves are being used to achieve this? Regular ball valves?

Stove top are like 3/4 turn gate valves to control the delivery of gas. Typically its about 3.5 inches of water collumn for natural gas and about 10 to 11 inches of water pressure for propane in residential servive. Enjoy, Woody

50mBar for a Camping Gaz on butane. Argos doesn't sell the regulators.

Do you mean 'regulate'?

On a typical gas system there is a regulator in or near the meter that brings the main gas line pressure down to an acceptable level for the house. In your stove, there is also a regulator that further reduces the pressure. Propane systems are similar as well.

A regulator uses spring force to open or close a valve to fix the pressure on the appliance side. Some of them can be adjusted to set the pressure. Typically on a stove it is fixed.

The pressure used depends on the appliance. High BTU appliances will need higher pressure, etc. For a stove, the installation manual should specify a range for the supply pressure.

Basically, what I am trying to understand is how the gas is modulated. If we were measuring the gas consumption at the gas meter, what kind of load profile would you see. Would it be a simple ON/OFF profile, or something close to that (i.e. within a repeatable range) or would it be modulated at the meter itself. I hope I am making myself clear.

To modulate …..What is turndown ratio?

Boiler turndown is a ratio of capacity at full fire to its lowest firing point before shut-down. Old boilers may have only two firing positions, low and high. Newer boilers fire over a wider range of capacities. Depending on the controls, there may be fixed setting points or fully variable settings. If a 1 million BTU boiler can fire as low as 100,000 BTUs, then it has a 10:1 turndown ratio. Turndown ratios are important for boilers that must operate over a wide range of capacities/ demands. In general, from an efficiency standpoint it is best to have the boiler sized to match the load. Boilers that have a wider turn-down ratio are therefore typically more efficient at meeting variable loads. However, there are exceptions, such as when it's possible to shut the boiler off for long periods of time, rather than run or cycle the boiler at very low fire conditions.

Turndown ratio and is it different for direct vs. indirect gas heaters?......

Turndown ratio compares the maximum to minimum heat output. Turndown ratio for direct gas burners is 25:1, which means that the burner can modulate from 4% to 100% of full fire. Indirect gas turndown ratio changes based on the controls. Example based on a single furnace unit (< 400 MBH). 4:1 electric modulation limits the heat output from 25% to 100% of full fire.

Gas stove ovens can have the supply to the burner modulated by temperature sensing which gives larger or smaller flame as required or they can shut down the flame completely when the set temperature is arrived at and open up again when the temperature falls to a set level [ hysteresis]. Burners on top of stove have a valve which can restrict the constant flow if required this controls the flame to a set level this is not referred to as modulated.

I cannot speak for stoves manufactured in the US but most if not all cookers as they are called in the UK and EC use the following controls:

1. Most hob burners are controlled between max and min firing rates by a simple 90 to 120º manual valve.
2. A limited number of hob burners are controlled by a thermostatic valve, the sensing element of which is in direct contact with the underside of the pan placed on the pan supports above the burner. The thermostatic valve may be of 2 types, but the only real difference is whether the fluid inside the system is a liquid or a gas. In ether case the valve consists of a sensing element in the form of a metallic bulb connected to a bellows capsule by small bore copper tube. The fluid in the bulb is heated by conduction from the underside of the pan and expands. The bellows is moved by this expansion and tends to close the gas valve reducing the heat input to burner until the temperature of the underside of the pan and the heat input are in equilibrium. It this stage the temperature ceases to rise and will stay constant unless the temperature of the pan is altered say by the addition of cold liquid. The fluid will then cool and reduce the pressure in the bellows allowing the valve to open and increase the flow of gas to the burner until equilibrium is attained again. There is usually a small fixed bypass drilling which allows the minimum amount of gas to pass through to the burner to keep it alight even when the thermostat is tuned down to minimum. This deals with the situation when the pan has been running at a high temperature and the thermostat is turned down to minimum.
3. All ovens (food for the roasting of) use a similar thermostatic valve with generally the same operating procedure. Older ovens use a rod type thermostatic valve. This uses the differential expansion of two metals to move the valve. The rod assembly consists of an outer sleeve fixed to the valve body with a rod fixed to the other end inside the tube. The fee end of the rod has the valve bob fixed to it The outer sleeve was often brass and the inner rod was a material called Invar which has a very low coefficient of expansion. As the brass sleeve is heated in the oven it expands and the lower expansion rate of the Invar results in the valve bob moving closer the valve seat reducing the flow of gas. There is a small fixed bypass drilling which allows the minimum amount of gas to pass through to the burner to keep it alight even when the thermostat is tuned down to minimum. This deals with the situation when thepan has been running at a high temperature and the thermostat is turned down to minimum.

As to gas pressures, the standard pressures world wide are 21mb (8"wg) for Natural Gas, 37mb (14"wg) for Propane and 6.4mb (2.5"wg) for Towns Gas. These pressures make burners interchangeable as far a fuel gas is concerned. If a burners is designed to work on Propane it will wotk on Natural gas with a jet size change and a reduced pressure.

The thermostats are not usually manufactured by the appliance manufacturer so I cannot quote an internal pressure within the bulb, bellows assembly but would expect it to be a few psi.

Here's a pic of a typical valve

the control is on the left, burner on top & fuel comes in on the right

I can't find a cut away drawing

the valve is modified ball valve design

a sleeve with a triangle shaped slot, to make it more adjustable, the mixing with with air, happening above, some stoves the air mixer is also adjustable...