import numpy
import matplotlib.pyplot as plt
import ammonia_props
amm = ammonia_props.AmmoniaProps()

0.8**20

0.011529215046068483

def bracket_p_min(x, p_low=0.002, p_high=0.2, max_iter=10):
    for i in range(max_iter):
        p = 0.5 * (p_low + p_high)
        try:
            state=amm.props2(x=x,P=p,Qu=0)
            # This p is valid, so reduce the upper bracket
            p_high = p
        except:
            # This p is invalid (too high), so set as lower bracket
            p_low = p
            
    return (p_low, p_high, state)

x_range = numpy.linspace(0,1,1001)
p_min = numpy.empty_like(x_range)
p_min.fill(numpy.nan)
t_out = p_min.copy()
for i, x in enumerate(x_range):
    p_low, p_high, state = bracket_p_min(x)
    p_min[i] = p_low
    t_out[i] = state.T

print(p_min.max())
p_above = p_min.max() * 1.1
t2 = amm.props2v(x=x_range,P=p_above,Qu=0,out='T')

0.17795703125

fig=plt.figure(figsize=(4,6))
ax1=fig.add_subplot(211)
#plt.xlabel('Ammonia mass fraction')
plt.ylabel('Minimum pressure (bar)\nbefore function fails')
plt.plot(x_range,p_min,'.')
ax2=fig.add_subplot(212,sharex=ax1)
#ax2 = ax1.twinx()
plt.xlabel('Ammonia mass fraction')
plt.ylabel('Temperature (K)\nof saturated liquid (Qu=0) ')
plt.plot(x_range,t_out,'.',label='At min pressure')
plt.plot(x_range,t2,'-',label='At p={:g} bar'.format(p_above))
plt.legend()
plt.show()

So, on my desktop, we can pull low pressure no less than 0.177957 bar.