Disclaimer: The following repair guide is provided for informational purposes. Not all these repairs have actually been tested here. iSoaker.com and its affiliates cannot and will not take any responsibility to any damages caused as a direct or indirect result of anything attempted. Use at your own risk/discretion.
Blasters belonging to the constant pressure system tech category include the SC500, CPS1000, and Monster. Water is put under pressure by pumping water from the reservoir into an elastic firing chamber. The volume of the firing chamber varies from blaster to blaster, but the use of an elastic chamber to pressure water allows for a much more consistent and powerful stream to be produced. The main drawback to this is that these types of blasters tend to run out of water much faster than their air-based cousins.
Pumping is difficult/impossibleIf the pump cannot be pushed or pulled (if applicable), its innards may have dried out and crusted. Try filling the reservoir with water and pulling/pushing harder on the pump. If it breaks, the blaster was useless anyhow.
If pumping is merely difficult, addition of some form of lubricant (i.e. Vaseline) to the pump shaft may help alleviate this problem.
Opting to open the weapon for a pumping problem usually does not help as the pump's shaft is typically sealed inside.
Pumping does not pressurize the firing chamberEnsure the reservoir has water.
Check the pump to see if it is still drawing water from the reservoir. If no water is beling moved when pumping, something may be blocking the water intake or the pump's seals may have worn down (in the latter case, repair the pump is usually not easily accomplished)
It is also possible that a tear has developed in the inner tubings between the reservoir and the firing chamber. If water is coming out of the housing of the blaster when pumping, an internal rupture is likely. In this case, one would need to open up the blaster and seek out the damaged part. Repair is often accomplished by either sealing the tear with hot glue and/or tape.
Blaster will not shootMake sure there is water in the reservoir and that the firing chamber is adequately pressurized. Try pulling the trigger harder.
Check the nozzle to make sure it is free of debris. If there is debris, attempt to clear the blockage by using a long needle/wire but be careful not the damage the nozzles or any of the blaster's inner-workings.
If using a blaster with multiple nozzle settings, ensure that the nozzle selector is properly aligned to the nozzle of choice and not in-between settings.
Blaster shoots mistThis could be the result of air inside the firing chamber. To clear this, pump up the firing chamber as much as possible, shake the blaster and fire straight up until only water is coming forth from the nozzle. Refill the reservoir to make up for the lost water.
Blaster continually shoots as soon as it is pressurizedAll models have an enclosed plastic valve system which cannot be opened. However, sometimes the problem here is that the pistons on the valve that the trigger tugs on have become dirty. Removing dirt from the pistons and adding on a little lubricating oil can often help this problem immensely.
Blaster leaks around the firing chamberHopefully, this is merely due to an inner piece of tubing coming loose. If this is the case, opening the blaster and seeking out the leak for repair with glue should fix the problem.
However, if the problem is due to a tear in the firing chamber, nothing much can be done to salvage the blaster.