In any pump, the important and critical factors are total head, speed, liquid properties, and pump arrangement. Excessive suction lift, shallow inlet submergence, or insufficient NPSHA, all spell a serious trouble from vibration, cavitation, lowered capacity, and reduced efficiency.
There are many causes of low suction pressure, including low indoor temperature, dirty filters, restricted ducts, undersized ducts, closed dampers, frosted coils, restricted refrigerant line, restricted piston, restricted strainer, and bad indoor evaporator motor. The list of reasons for this is extensive.
The first thing to check is the valve. If the valve isn't properly in place, there will be no suction. It's possible that the valve has a tear; even a small tear can lead to suction loss. It's generally recommended to replace valves every three to six months for this reason.
If the water pump is running but no fluid is being pumped this could be blocked inlet suction filter, check valves failed with pumps bypassing, blocked discharge lines, electric motor polarity is incorrect or incorrect pressure settings parameters amongst other issues.
Ensure that the pipe diameter is adequate to handle the desired flow rate and minimize pressure drops. Minimize bends and use smooth pipe materials to reduce friction. Proper hydraulic design will help maximize the available suction pressure and improve pump performance.
Final answer:
Several conditions can lead to a decrease in suction pressure in HVAC systems, including a restricted liquid line filter drier, a dirty indoor air filter, and an underfeeding metering device. Each of these factors affects refrigerant flow and heat absorption processes.
Improper inlet conditions are one of the most common reason pumps fail to produce their expect pressure. Inlet issues may also cause ongoing reliability problems. One culprit is air entrainment or lack of prime. It is important to make sure that system is designed so that liquid floods the pump to prime it.
Overcharging leads to overfeeding the evaporator with refrigerant, which leads to higher suction pressure. Another possibility is having oversized EXV causes an overfeed to the evaporate, which increases your suction pressure.
A pressure reducing valve creates and holds a downstream pressure set point. Oil and gas producers use a pressure reducing valve (also called a "pressure reducing regulator") as a suction controller or recirculation valve on a compressor, or to supply fuel gas.
Pump efficiency is determined by principally two parameters, head and flow rate, in addition to other factors such as properties of the fluid, impeller design and motor speed selected. where T is the torque, Nm; w is the angular velocity, rad/s.
The factors examined separately include system capacity, refrigerant type, evaporator and compressor elevation difference, and suction line length.
These include checking the vertical suction lift, total head lift, priming of the pump, ensuring that the suction hose and strainer are submerged and not obstructed, verifying that the suction and discharge hose or port is not leaking air or water, ensuring that the discharge hose is not blocked or restricted, and ...
Entrained air or gas/vapor can have a detrimental effect on the suction performance of a pump. Air or gas will expand in the inlet of the impeller, which blocks the liquid flow through the impeller, much like the blockage from cavitation vapor bubbles, both of which cause a decay in the pump discharge pressure.
Your Pressure Switch Has Malfunctioned
One of the most common reasons why the pump might be running, but you don't have any water going to your house, is that there is a malfunction with the pressure switch itself. If you take a look at the pressure tank, you will see a pressure switch at the bottom.
If you want to increase the hydraulic pump pressure in your system, there are a few things you can do. First, you can increase the fluid flow rate into the pump. This will increase the pressure on the fluid, and therefore increase the output pressure of the pump. Second, you can increase the displacement of the pump.
A change in sound can alert you to an issue with your pump or system. If you hear popping sounds, especially near the impeller, you could be experiencing cavitation. This occurs when there are pressure changes within a liquid, causing tiny pockets of air to form and then implode.
Apart from refrigerant leaks causing loss of critical charge, the most common problem associated with low suction pressure is: LOW LOAD, i.e., not enough warm, moisture laden airflow across the evaporator coil. Classic causes: Undersized duct or poorly designed and/or poorly installed air distribution system.
Increased Suction Pressure
In a capillary configuration, an overcharged system will function at a higher suction pressure than designed. This is attributed to the greater mass flow rate of refrigerant into the evaporator. This means that more liquid molecules are available to change phase to gas than usual.
While air may look like it's moving from the backflow protector, if the valve isn't in place, there will not be suction. If you've confirmed the valve is in place, look to see if there is a tear somewhere in it. Even just a small tear or disformed piece of the valve can cause you to lose suction.
When You're in a Pinch, Turn to Petroleum Jelly. If your clean and boiled suction cups are still not sticking, try adding petroleum jelly to their suction surface. Now when you press on the suction cups, the jelly will fill any gaps between the surface and the cup, eliminating any pesky air bubbles.